Research on water institutions belongs to the broader scope of research on the political economy of water governance. That scope is enormous and growing, as surveyed in recent volumes by Burnett et al. (2014), Conca and Weinthal (2018), Harris et al. (2019), Bogardi et al. (2021), and others. The historiographical perspective offered here thus focuses directly on institutions, and considers related lines of water politics as they arise.

The word institution has ancient origins, stemming from the Latin institutio (“set up”), and has early English usage in Thomas More's Utopia, translated in 1551, where it refers to regulative social norms and laws. Research on water institutions that influenced the United States dates to mid-19th century studies of irrigation systems in the Andalusian region of Spain. Those historic systems developed community water rights and tribunals to adjudicate disputes among water rights holders that date back to medieval times (Glick, 1970). They were studied as successful irrigation precedents by British colonial engineers in India (Garrido, 2014), and Californian engineers and lawyers who compiled surveys of irrigation laws from around the world (e.g., Hall, 1886). A century later a political scientist and economist, Maass and Anderson (1978), compared the economic efficiency and equity of three of these Spanish systems with three irrigation systems in the western U.S. While some eastern U.S. politician-scholars like George Perkins Marsh criticized the social and environmental effects of irrigation, western engineers like Mead (1903) believed irrigation institutions would enable the progressive reclamation of arid lands for small farmers. A smaller body of scholarship at that time wrote of health spas and bath facilities, i.e., organizations, as “water institutions.” By the turn of the last century, the term institutions thus denoted water rights, reclamation policies, and a wide range of water organizations.

The mid-20th century witnessed a wave of critical political scientific research on water institutions, especially those of federal river engineering and basin development (Wengert, 1957). Early case studies featured the unique federal corporation known as the Tennessee Valley Authority (Selznick, 1949). Maass (1951) wrote a deeply critical account of Muddy Waters: The Army Corps of Engineers and the Nation's Rivers. Outside the U.S., Wittfogel (1957) directed stronger criticisms of centralized irrigation regimes that he described as Oriental Despotism – from antiquity to the present—though oddly omitting U.S. case studies (cf. Worster, 1992; Wescoat, 2000).

Early research on water politics in the western U.S. included Dean Mann's (1963) study of state water policy in Arizona. Political scientist Ostrom (1953) analyzed the politics of metropolitan water systems, which he characterized as polycentric rather than as centralized (Ostrom et al., 1961). Ostrom (1990, 2005, 2010) carried forward that line of research on polycentric dimensions of political economy and related concepts of institutional diversity.

Although studies of water institutions became mainstream in the decades that followed [Smith, 1960; Federal Council for Science and Technology (U.S.), 1969; Fox, 1976], there were growing concerns about both the subfield and the problems it needed to address. Ingram et al. (1984) described institutional studies as more descriptive than analytical. Institutional problems ranged from fragmentation across water sectors to rigid hierarchical structures of control, intractable stakeholder conflicts, and persistent constraints on social change (Ingram and Ullery, 1980). These criticisms helped spur an international literature on strategies for institutional reform (e.g., Gopalakrishnan et al., 2005; Saleth and Dinar, 2005; Crase and Gandhi, 2009).

On the broader plane of institutional economics, advances were made in linking research on economic history and political economic change (North, 1990, 1991), which included many applications to property rights, common property regimes, and environmental policy evaluation (Saleth and Dinar, 2004). Anthropologist Douglas (1986) critiqued rational choice models of institutions, arguing that societies construct institutions to support cooperation. In between these views, political scientists Elinor and Victor Ostrom developed a framework of Institutional Analysis and Design (IAD) that focuses on institutions as informal rules-in-use rather than as formal written documents. An important application of that framework involved the crafting of institutions for self-governing irrigation systems (Ostrom, 1992), which built upon earlier comparisons of bottom-up community water systems and top-down bureaucratically managed systems (e.g., Coward, 1980). Cole (2017) argues for including formal laws within the IAD framework. Recent research treats these institutional hierarchies as multi-level systems, which has special relevance for the Colorado River basin region (e.g., Moss and Newig, 2010; and for the Colorado see York, 2021).

Most recently, theorists have generated research on the dynamic social and political nature of institutions (e.g., Guala, 2016; Philosophy of the Social Sciences, 2018; Jupille and Caporaso, 2022). Recent water resources research does not appear to cite these works yet, which may reflect a shift from institutions toward the expansive theme of governance (Woodhouse and Muller, 2017). However, a focus on institutional levels of water management promises insights into their origins, logic, and interactions. The historical geographic approach taken here shows how institutional levels of water management in the Colorado River basin region—from the community to international level – co-evolved with changing ideas about the enabling and constraining, regulative and reforming, dimensions of water institutions. An important step in the context of this journal issue on scale is to consider the relationships among institutional levels and geographic scales of water inquiry.

A core argument in this paper is that water management institutions develop at different socially-defined levels, from communities to states and nation states. It is important to consider how these institutional levels are related to geographical scales of water inquiry (for related but somewhat different perspectives on levels and scales see Sheppard and McMaster, 2004; Neumann, 2009; Islam and Susskind, 2013, p. 46–51, 71–79; York, 2021). Institutional levels are socially-defined jurisdictions with distinctive rules and organizations that guide water management. They include community water norms, state water rights, interstate river compacts, tribal water laws, federal water policies, and international water treaties. Complex river basins, like the Colorado, have all of these multiple levels of water management (Wheeler et al., 2018; York et al., 2019). Although often described hierarchically, whereby international treaty agreements take precedence over federal policies, which take precedence over state and local policies, local actors retain significant authority and agency in river basin deliberations. Over time, each level shapes and is shaped by all of the others, while retaining and adapting its own distinctive rules and organizational structures.

It will be shown that community (including tribal) levels arose first, followed by state, interstate, federal, and international levels in successively larger geographical areas. This progression calls for consideration of relationships between institutional levels and geographic scales. For example, the state level of water laws applies to geographical configurations of water use and hydrologic processes within the jurisdiction of a state. However, those water patterns and processes can be examined at multiple geographical scales that do not correspond or fall within institutional boundaries. Hydrologists analyze variations within and across scales in quantitative ways (e.g., Sposito, 1998). Social scientists, by comparison, have focused recently on the politics of scale (Norman et al., 2012, 2015; Perramond, 2012, 2015); political dynamics across scales (Mumme and Leigh Taylor, 2014); and political ecologies that encompass multiple spatial and temporal scales (Ward, 2003; Buechler and Hanson, 2015). These political approaches challenge the “fixity” of scale (Martin, 1999) and “stationarity” of water rights and compacts (Perramond, 2020). At the same time, they tend to conflate institutional levels and geographical scales of water inquiry.

Sometimes efforts are made to align levels and scales, as for example when a state water agency uses river basins, watersheds, or economic regions to administer water rights or water policies in those areas. As water users compete with one another over transboundary streams and aquifers, states develop higher-level interstate institutions to address those larger geographical issues. In the Colorado River basin context, its multi-level system of institutions is collectively known as the “law of the river” (MacDonnell et al., 1995).

The argument in this paper is that a systematic review of levels of water management helps understand the institutional logic at each level. Understanding the multiple levels of institutions that develop in the historical geography of a river basin region sheds light on basin challenges and opportunities. There are several ways to construct a multi-level review (e.g., see York, 2021). Many studies start with a pressing water problem, and review its institutional context starting at the international treaty level and proceeding to the federal policies, interstate compacts, state laws, and local organizations that define the problem (e.g., Wescoat, 1984, 25–58 on oil shale development; and Wescoat, 1986 on salinity). This top-down progression from relatively recent international water institutions to lower level institutions that have earlier histories cuts against the grain of history.

A second approach in river basin histories thus proceeds in the opposite direction. It may begin with a current situation or problem in the basin, but it strives to reconstruct the origins and development of relevant water management institutions over time. Historians have offered rich accounts of western water management from early records of Hispanic and 19th century colonization, followed by 20th century river basin development (e.g., Meyer, 1984; Worster, 1992). This historical approach tends to either proceed from local water communities to changing state, federal, and international policies; or, more commonly, it retraces the dynamic interactions across multiple levels of water management over time. Historians often focus in depth on institutional changes over relatively limited time periods, e.g., negotiations over the Colorado River compact in the early 20th century (Hundley, 2009). Their longue durée rarely extends to the archaeological record of prehistoric water management that is important in the Colorado River basin.

A third approach comes from water lawyers in the western U.S. who recount the institutional history and trajectory of the “law of the river,” often beginning with basin state water laws, followed by documents that shaped the Colorado River Compact in 1922, and subsequent laws and policies up to the present (e.g., MacDonnell, 2021). Some legal histories mention prehistoric and early Hispanic communities (Meyer, 1984; Ragsdale, 1998), but most begin with late-19th century water laws. Water law casebooks are often organized by these state, interstate, federal, and international levels (e.g., Benson et al., 2021; Zellmer and Amos, 2021).

This paper builds upon these three approaches, especially the “law of the river” tradition, by presenting a systematic review of levels of water management in the Colorado River basin region. It shows how rules and organizations at each level differ from, and relate to, those above and below. It extends the law of the river approach by adopting a macro-historical geographic approach that proceeds from community water institutions that are early in time and small in size to institutional levels that are larger in size and more recent in time. Within the constraints of a journal article, it is only possible to offer a brief review of research conducted on each institutional level of water management. The paper used bibliographic search methods described in the next section to identify sources for each level that are summarized in the results section. The discussion reflects on interactions among levels and the conclusion on insights from this review.

Many studies have dealt in colloquial terms with levels of water management in the Colorado River basin (e.g., local level, village level, state level, and so on), but few treat the concept of levels systematically. An early study by Larson et al. (1979) shows how levels of decision making in the Uintah basin and Colorado River basin dealt with 20 obstacles to conflict resolution in water resources planning. Moore (2017) examines how interactions at the subnational level of state and non-state actors affect collaboration in federal river basins like the Colorado. Several studies employ concepts of multi-level water management. York et al. (2019) consider the concept of a nested hierarchy as one of three lenses for understanding the socio-hydrology of Arizona water resources. Evans et al. (1982) developed an early multi-level model for salinity control in the Upper Colorado Basin. Aghnami and Hogue (2005) discuss computational strategies for model calibration in multi-level watershed hydrology. Wheeler et al. (2018) compare methods of multi-level modeling with applications to the Colorado and Murray-Darling River basins. Suykens (2018) explicitly frames the “law of the river” as a multi-level system. Several studies examine decision-making processes at multiple levels in relation to sustainability criteria (Berggren J., 2018; Iribarnegaray et al., 2021; York, 2021).

As mentioned above, institutional levels are often conflated with concepts of scale in water resources research. This bibliographic search yielded larger numbers of keyword and title hits for scale than for levels. Many of those hits describe research of a specific size, e.g., small-scale, large-scale, landscape scale, and so on (e.g., Huenneke et al., 2015). The largest group of studies involve scale in hydrological and ecological vis-à-vis management terms. Some focus on downscaling climate models to generate hydroclimatic scenarios (Freeman, 1993; Kim et al., 2006; Mendoza, 2015; Foster, 2018). Others analyze temporal and spatial scales of streamflow, peak flow, stream networks, and watershed hydrology (Peckham, 1995; Veitzer, 1999; Mantilla, 2007; Nowak, 2011; Ficklin et al., 2013). Studies of ecological scale examine riparian and aquatic species and community dynamics (Lammers, 1998; Shafroth et al., 2017), and ecosystem threats (Paukert et al., 2011; Comte et al., 2022). An interesting law review article assesses what water lawyers can learn from large-scale ecological research (Bosselman, 2002).

Another significant group of studies deal with scales of water management in the Colorado River basin. Page and Dilling (2019) ask how “communities of practice” can help scale-up the use of climate information in water management. Several studies examine multi-scalar dynamics of water quantity and quality issues along the U.S.-Mexico border (e.g., Mumme, 2008; Mumme and Leigh Taylor, 2014). Fischhendler and Feitelson (2003) underscore how U.S.-Mexico negotiations on Colorado flows were linked to the larger border region that includes the Rio Grande and Tijuana River basins. Fraley (2012/2013) reviews challenges of “scaled legislation” that has promoted regional development in the Colorado River basin from the New Deal era to the present. A recent study re-reads 19th century natural surveys of the Colorado River “from source to sea” through the politics of scale (Kroepsch et al., 2021).

The most common approach to levels of water management in the Colorado River basin involves various types of policy analysis that situate urban, regional and subsectoral water policies within broader sociopolitical contexts (e.g., Al-Sabbry, 1998; Gerlak, 2017; Karambelkar, 2020). Colorado River Simulation System (CRSS) models using the Riverware platform incorporate institutional rules for reservoir operations to simulate the effects of hydroclimatic and policy scenarios (Fulp et al., 1999; Zagona et al., 2001; Gilmore et al., 2004; Gastélum and Cullom, 2013; and a critique by Wheeler et al., 2019). Hadjimichael et al. (2020) model the distributional effects of institutional variables within the basin.

Institutional analysis has been employed to characterize water laws and policies in the basin (e.g., Kenney, 1995; Lord et al., 1995; Kenney et al., 2011). This is the principal approach used in research on the law of the river, which involves structured analyses of Colorado River laws, compacts, and treaties (Fahmy et al., 1983; MacDonnell et al., 1995; Anderson, 2004; Harkins and Snow, 2004; CLE International, 2013; Robison, 2017, 2022). State and federal agencies have produced compilations of the law of the river documents (e.g., Arizona Department of Water Resources, 2000; U.S. Bureau of Reclamation, 2010). In addition to descriptive and analytical studies, some law of the river research advances normative proposals for river basin management (e.g., Quesada, 2016; McKenzie, 2021, on the neighboring middle Rio Grande). MacDonnell (2021) offers an upper basin perspective on concerns about institutional uncertainties in the law of the river (also Carrico, 2014).

Institutional research is increasingly framed within the broader socio-political context of water governance (e.g., Getches, 1997; Koebele, 2017; Berggren J. G., 2018; Singh et al., 2019; Juricich, 2020). Governance research in Arizona, for example, has focused on pressing issues of groundwater and transboundary water management (e.g., Wilder, 2020; Albrecht, 2021). Burnham (2022) employs discourse analysis in a study of the Central Arizona Project. Several studies employ a political ecological framework to examine power relations across boundaries in the lower Colorado (Ward, 2003; Butler, 2015; Scarrow, 2016). A significant body of governance research addresses transboundary relationships (e.g., Sternlieb, 2014; Mead, 2017; Tapia Villaseñor, 2020). Institutional levels of water management are incorporated in most of this governance research.

With this demonstration of bibliographic search methods applied to levels, scales, institutions, and governance of the Colorado River basin region—and the rationale for focusing on institutional levels—we proceed to substantive results and review. Given the breadth of review, the results are necessarily limited to major institutional structures and references.

Communities constitute the earliest and most local level of water management from prehistoric times to the present. The community level includes four major historical periods and culture groups in the Colorado River basin region—from prehistoric times to the present – each of which has distinctive institutions and continuities that have shaped subsequent multi-level systems of water management.

Constitutionally, water is a state subject in federal governments like the United States and Mexico, which means that states have primary jurisdiction over water matters within their boundaries. Portions of seven states lie within the Colorado River basin in the United States and two in Mexico. It is fascinating to compare these state and basin boundaries (Figure 1). Southwestern Wyoming has a relatively small sparsely populated grazing and mining area of the basin's headwaters. The western half of Colorado has the headwaters of four regional river basins that support irrigation agriculture, energy, and recreational uses. It also exports water across the Rocky Mountains to irrigated and rapidly urbanizing basins in eastern Colorado. New Mexico has the San Juan River basin in its northwest corner and arid headwaters along its western border. It exports water from the San Juan River basin into the Chama tributary of the Rio Grande valley. Utah receives headwater flows from Colorado, Wyoming, and New Mexico. It exports water from the Colorado River across the Wasatch Mountains into the intensively irrigated interior drainage of the Great Salt Lake Basin. Each of these states has promoted transbasin exports within state boundaries to maximize its use of Colorado River basin waters.

The three lower basin states include hydrologically small contributions from Nevada and California, though those states have politically powerful water users. The extrabasin region of southern California receives massive water transfers via the Colorado River Aqueduct and All-American Canal. Arizona is the one state that lies almost entirely within the basin. It receives a long-distance water transfer from the main stem of the Colorado through the Central Arizona Project canal. A small area of Sonora state in Mexico drains into the Santa Cruz watershed at Nogales, Arizona (Ingram et al., 1995). A small area of northern Baja California state drains into the New River and Salton Sea from the Mexicali area (Dicochea, 2010), and also into the shared Tijuana River that discharges into the Pacific Ocean. Sonora and Baja California share the lowest reach of the Colorado River before it discharges into the depleted and degraded Colorado River delta and Sea of Cortez (Ward, 2003).

With the exception of California's early statehood in 1850, basin states were initially established as territories that were nevertheless empowered to pass water statutes and decide legal cases. They became states between 1864 (Nevada) and 1912 (Arizona and New Mexico) (Supplementary Table 3). The bibliographic search at this level, and those that follow, gave more attention to Lexis/Nexis legal databases that include law reviews, cases, and statutes. The America History and Life and Web of Science databases were omitted as less focused on water policy at these levels. Search terms included the seven basin state names and “water law” or “water policy” (see Supplementary Table 4).

Each state has guides to its water laws for professional and public use [e.g., CLE International, 2013; Howard and Alstead, 2009 (Nevada); MacDonnell, 2014 (Wyoming); Hobbs and Colorado Foundation for Water Education, 2018 (Colorado); Liebert, 2019 (California)]. Given the importance of legal precedents in state water law, histories of those laws have been compiled in legal treatises, books, and reviews [e.g., Reich, 1995 (Arizona); Kanazawa, 1998, 2015 (California); Harrison, 2001 (Nevada); Olds, 2004 (Utah); MacKinnon, 2006 (Wyoming); Hall, 2008 (New Mexico); Walston, 2008 (California); Schorr, 2012 (Colorado); Bennion, 2014; Hundley, 2020 (California)].

The prior appropriation doctrine became an important principle in state water laws that defined water rights institutions in the latter part of the 19th century. Colloquially termed “first in time, first in right,” it stipulates that in the event of scarcity water rights holders must divert water in the order of their “seniority” (i.e., the date when they put water to a “beneficial use”). Prior appropriation had its origins in mining camps where miners diverted water from stream channels to their mineral claims. Early users had priority over later ones, which was adopted as a legal precedent in Irwin v. Phillips (5 Cal. 140, 1855) on federal lands in California, and in mining districts of Colorado (Schorr, 2012, ch. 1). Colorado courts extended the prior appropriation rule to irrigation water rights, rejecting the riparian rule of reasonable use among streamside land owners, which governed in the eastern United States. The Colorado case of Coffin v. Left Hand Ditch (6 Colo. 443) ruled that the historical time of use established the basis of a water right, rather than the riparian place of use, even when senior uses lay outside the basin of origin but within state boundaries. The Colorado Doctrine (Schorr, 2012), as it was called, was adapted in all of the other basin states, except California. The California case of Lux v. Haggin (69 Cal. 255, 1886) ruled that prior appropriation must allow for some reasonable use by downstream riparian claimants, which led to a hybrid system of surface water laws. That hybrid arrangement was adopted by other Pacific coast and Great Plains states.

Colorado also stood out for water articles in its 1876 State Constitution that declared:

Not surprisingly, this constitutional right to divert all waters of natural streams in the state led to overappropriation. Wyoming adopted similar language in 1889 with the more flexible provision that, “No appropriation shall be denied except when such denial is demanded by the public interests” (Art's. I, 31 & VIII, 1, 3). Over the past century, state water laws have addressed whether a “diversion” is required to establish a water right, what constitutes a “beneficial use,” and how to limit “waste.” They differ as to whether and how appropriations can be made for instream flows for environmental, aesthetic, and recreational uses; and for on-site use of diffuse surface flows [Elliott, 2011; Connell, 2019 (Wyoming); Hobbs, 2019 (Colorado); Matheson, 2004 (Utah)]. The states have refined methods for estimating water use efficiency, conservation, and waste [Glennon, 2018 (Arizona); Zisch, 2014 (Wyoming)]. Transbasin “developed water”, for example, can be reused and recycled within the state, provided its water right is in priority in its basin of origin [City and County of Denver v. Fulton Irrigation Ditch Co., 179 Colo. 47, 506 P.2d 144 (1972) (cf. Fuller, 2014 (Wyoming)].

States vary in their procedure for establishing a water right, which generally begins with an expression of intent to appropriate, followed by diligence in developing the right, putting the water to a beneficial use, and fulfilling any recording steps that may be required. Once developed, a right must be put to continuing beneficial use, the standards of which can evolve with increased competition and standards (Clegg, 2005; Hobbs, 2013; MacDonnell, 2015). Some states permit filings of conditional water rights, especially by cities, in anticipation of increased future water demand. For those rights the priority dates back to the time of filing rather than the later time of beneficial use [e.g., City & County of Denver v. Sheriff, 96 P.2d 836, 839 (Colo. 1939)]. This controversial policy can contribute to water rights uncertainty and overappropriation. When a senior water right does not receive its full amount, a “call” is placed on the river that requires all users to divert only their decreed amounts, at which point the most junior users are shut off until more senior uses are fully served.

States allow changes of water rights to meet new demands subject to two rules. First, changes are limited to the “historical beneficial use” of the right – any claim beyond that amount reverts to the water rights priority queue or the stream. Second, the proposed change must cause “no-injury” to any other water right holder in the system, junior or senior, whether by changes in withdrawals, place of use, or return flows (Banks and Nichols, 2015). Wyoming initially forbade water transfers as speculative but later allowed them (MacKinnon, 2006; on anti-speculation see Cannon, 2009; Schorr, 2012; Hobbs, 2013). These rules and procedures for changing a water right can have substantial transaction costs, particularly in states like Colorado where changes are reviewed in special water courts, as compared to states where the state engineer's office evaluates proposed changes (National Research Council, 1992; Womble and Hanemann, 2020). States differ on how one can lose a water right, e.g., through cancellation, forfeiture, or abandonment, though they have been reticent to implement those provisions in areas of the Colorado River basin seeking to develop a state's share of the river (Zellmer and Amos, 2021, p. 165–70).

Where states differ most is in their groundwater laws and their approaches to conjunctive management of surface and groundwater resources (DuMars, 1985; Meyer, 1989; Avery et al., 2007; Ruple, 2011; Meldrum, 2013). California developed a concept of correlative groundwater rights whereby rights are proportionate to one's land ownership above the aquifer [Katz v. Walkinshaw, 74 P. 766, 772 (Cal. 1903)] and historical levels of pumping. Colorado adapted prior appropriation for groundwater deemed tributary to streamflow; and state permitting of “non-tributary groundwater” [State Dep't of Natural Res. v. Southwestern Colorado Water Conservation Dist., 671 P.2d 1294 (Colo. 1983)]. Most states have developed some form of pumping permits, with historical exceptions for domestic wells (Zellmer and Amos, 2021, p. 242–6). Groundwater use for energy development (e.g., shale oil or fracking) have posed new legal as well as environmental issues that include groundwater contamination, overdraft, subsidence, and air pollution [cf. Ariz. Rev. Stat. Ann. §45–401, 596(I); and Colo. Rev. Stat. §37–91–110; Ruple and Keiter, 2010; Ritchie, 2014; Whitney-Williams and Hoffmann, 2015].

All of the basin states initially relied on a State Engineer to administer water rights, i.e., to record perfected rights and physically turn off junior rights in times of scarcity. By the mid-20th century, however, growing water competition and environmental conflict led some basin states to create broader departments or divisions of water resources management. As noted above, Colorado stands out for its heavy reliance on water courts in its seven regional water divisions, four of which are headwaters basins of the Colorado River (i.e., the Yampa, Colorado, Gunnison, and Animas-La Plata headwaters). Not surprisingly, Colorado has the largest body of water rights case law (Supplementary Table 2D), as well as high transaction costs associated with water rights changes and transfers (National Research Council, 1992; Womble and Hanemann, 2020).

Notwithstanding the variations noted above, the prior appropriation doctrine distinguishes the state level of water management from institutions at other levels in the basin. State water laws have evolved to address myriad issues within their boundaries. States engage in intense internal debates about property rights in water (Benson, 2012; MacDonnell, 2015), but passionately defend those property rights institutions against encroachment by other states or federal organizations (Schorr, 2012). When states come into conflict with one another over transboundary waters, they turn to the interstate level of water management.

Interstate relations constitute the next higher institutional level of water management. They have their own institutional logic and organizations distinct from those of the participating states. Three types of interstate apportionment have developed in the Colorado River basin: (1) interstate litigation; (2) interstate compacts; and (3) Congressional apportionment. In each case, the US. Constitution stipulates involvement of the federal government. Bibliographic search terms for this level were “interstate” or “compact” and “Colorado River,” again with increased emphasis on law reviews and legal sources (see Supplementary Table 5).

The federal level has been mentioned on multiple occasions above, and notwithstanding state jurisdiction over many water matters, federal institutions have broad importance for the Colorado River basin region. The US Constitution stipulates federal powers of water management that include the:

The bibliographic search at this level involved the same sources as in previous sections, plus websites of major federal agencies involved in the region. The results are so broad in scope and rich in content that we can only outline some of the major elements here. Federal agency programs are complicated by non-overlapping regional boundaries. For example, those of the US Department of Interior, which is most directly involved in basin management, combine the Upper Colorado with the Upper Rio Grande rather than with the Lower Colorado basin; while other agencies have different regional boundaries (Figure 4).

By way of background, most of the Colorado River basin region became part of the United States and subject to federal laws through the Mexico Cession of 1848 and Gadsden Purchase of 1854. The Indian Appropriations Act of 1851 provided for reservations with limited sovereignty for Indian tribes. While territories, states, and reservations were being created, the federal government undertook a series of explorations of the Colorado River led by John Wesley Powell (1875) in 1869–1872 (Robison et al., 2020). Scientific surveys of this period also started to refer to the Colorado as a “basin” (e.g., Macomb and Newberry, 1876).

A movement promoting irrigation in the western states in the late-19th century led Congress to pass the Reclamation Act of 1902, which established a Reclamation Service (later the Bureau of Reclamation) under the U.S. Geological Survey (Lee, 1980; Pisani, 1992; Worster, 1992). The Act provided for federal reclamation projects for farms <160 acres in size, though that socio-economic policy would later be abandoned. Irrigation Investigations led by the U.S. Department of Agriculture Office of Experiment Stations identified potential project locations and beneficiaries. The Salt River Project (2017) in central Arizona was one of the first US Bureau of Reclamation projects in the Colorado River basin, authorized in 1903. It funded a large masonry dam and canal construction, some of which followed the prehistoric Hohokam canal alignments (Heslop, 2012).

When Congress passed the Boulder Canyon Project Act in 1928, it greatly increased the scale of federal dam construction including the massive multi-purpose Hoover Dam and All-American Canal across southern California. It empowered the Secretary of Interior to manage lower basin reservoir deliveries, which became the institutional basis for federal river operations and, recently, federally-mandated cutbacks in 2022. In 1937, the Bureau of Reclamation began work on the large Colorado-Big Thompson Project that transferred supplemental water from the upper Colorado River basin to the South Platte River basin in eastern Colorado. The Boulder Canyon Project Adjustment Act of 1940 financed dams in the upper and lower Colorado basins in part by using hydropower revenues from Hoover Dam. The Colorado River Project Storage Act of 1954 added five additional large upper basin dam projects—(1) Glen Canyon Dam on the Colorado River in Arizona; (2) Flaming Gorge Dam on the Green River in Wyoming; (3) Curecanti Dam on the Gunnison River in Colorado; (4) Navajo Dam in New Mexico; and (5) the Central Utah Project—i.e., one dam for each upper basin state. These large dams helped fulfill the upper basin's compact obligation while enabling them to physically develop their own compact-apportioned shares. It did so in part by providing for 16 small “participating projects” and another 19 potential participating projects, financed in part by hydropower revenues from the large hydropower projects.

The last massive federal infrastructure project came in 1968 with the Colorado River Project Act that among other things authorized the 336-mile-long Central Arizona Project from the lower Colorado River to central and southern Arizona. The 1968 Act stipulated that Central Arizona Project waters are subordinate to California's 4.4 million acre-feet entitlement (under the Boulder Canyon Project Act)—provisions that became relevant in the 2022 drought cutbacks. The Act omitted a large dam proposed for the sublime Marble Canyon of the Colorado River, which signaled the ascent of environmental values and decline of large dam construction (Reisner, 1993; Summitt, 2013; Perramond, 2018; Di Baldassarre et al., 2021).

Environmental opposition to large dams coalesced with the implementation of new federal laws and agency regulations. All proposed federal actions are subject to environmental impact assessment under the National Environmental Policy Act of 1969 (42 U.S.C. 4321-4347, January 1, 1970, as amended). Legislation protecting endangered plant, animal, and fish species led to greater roles for the US Fish and Wildlife Service under the Endangered Species Act (16 U.S.C. 1531-1544, as amended). The Clean Water Act of 1972 (33 U.S.C. §1251 et seq.) included water quality regulations implemented by the U.S. Environmental Protection Agency and wetlands protection permitting by the U.S. Army Corps of Engineers. Large federal lands are managed by the Forest Service, Bureau of Land Management, National Park Service, and others. Energy crises in the 1970s led to transfer of the Bureau of Reclamation's hydropower role to the Department of Energy's Western Area Power Alliance in 1977.

In addition to their expanding regulatory roles, Federal agencies claimed “reserved rights” for water on national lands that were legislatively set aside for forests, parks, grazing, and other uses (Federal Power Commission v. Oregon, 349 U.S. 435, 1955). In a series of cases the U.S. Supreme Court stipulated that reserved rights are based on the central purpose of the lands reserved with water rights priorities dating to the time of their establishment (U.S. v. New Mexico, 438 U.S. 696, 1978).

There was a major attempt to coordinate these diverse federal water roles through the Water Resources Planning Act of 1965 (P.L. 89-80), which established a national Water Resources Council, regional River Basin Commissions, and Principles and Standards for Planning Water and Related Land Resources that adopted four accounts for evaluating federal projects: (1) national economic development, (2) regional economic development, (3) environmental effects, and (4) other social effects. However, these reforms were reversed in 1983, revisited in 2009, and updated in 2015, albeit on a level far short of integrated national water policy and planning.

In the absence of nationwide water policy, the Department of Interior's Bureau of Reclamation has the lead federal role in Colorado River basin operations. It prepares monthly 24-month model runs, drought contingency planning, and basinwide policy analysis (U.S. Bureau of Reclamation, 2019, 2022; U.S. Department of Interior, 2022). In the 2022 drought emergency, for example, the Secretary of Interior invited states to prepare a voluntary drought reduction plan. The Upper Colorado River Commission (2022) presented a five-point plan, but when the lower basin states were unable to agree, the Secretary announced 2023 cutbacks of 592,000 acre-feet in Arizona; 25,000 acre-feet in Nevada; 104,000 acre-feet in Mexico; and none for California (based on the 1968 Colorado River Project Act) (U.S. Department of Interior, 2022). The California Colorado River Board (2022) offered 400,000 acre-feet of conservation measures through 2026, and negotiations continue.

What distinguishes the federal level from levels below are its constitutional role in interstate relations, river basin development, treaty-making authority with Mexico, and trust responsibility with Indian tribes. Most federal policies and projects thus entail multi-level stakeholder processes, with greater or lesser degrees of inclusion, historically greater for the basin states and lesser for Indian tribes as elaborated below.

American Indian tribes have operated at every institutional level of water management in the Colorado River basin from prehistoric communities to historical interactions with Hispanic and Anglo communities, basin states, and the United States—processes that involved dispossession and relocation to reservation lands slowly leading toward Indian reserved water rights. The tribal level is quasi-national as tribes have sovereignty over their lands, waters and institutions. However, the U.S. federal government has a trust responsibility for tribal interests that affects their water institutions.

There are thirty federally recognized tribes within the Colorado River basin (Figure 5). Their reservations vary in spatial scale from the large transboundary reservation of the Navajo Nation, which surrounds the Hopi reservation in northeastern Arizona, to smaller reservations within each state of the basin except Wyoming. The basin's largest number of tribes and area of reservations lie in Arizona. This bibliographic search followed previous conventions with an emphasis on law review articles and cases. The search terms “Colorado River” and “tribe” or “tribal” yielded rich results. “Colorado River” and “Indian” was fruitful, though it gave a disproportionate number of hits on Colorado River Indian Tribes who live on the banks of the lower Colorado in Arizona and California, two of which have longstanding roots on those lands (Mohave, Chemehuevi), while two tribal groups have modern resettlement histories (Hopi and Navajo) (Blossom, 1979; Caylor, 1996; Ramirez, 2019).

It has long been recognized at other levels that tribal water rights would eventually be recognized, adjudicated, and developed, but fulfillment of those obligations has lagged for decades. Several aspects of Indian water rights distinguish tribal water institutions from water rights at the state level (Zellmer and Amos, 2021, p. 372–84). The case of United States v. Winans (198 U.S. 371, 384, 1905) in the Pacific northwest recognized aboriginal tribal rights for fishing that were not granted away or lost by treaty with the United States. As aboriginal rights, they have priority dates that are time immemorial, and thus intrinsically senior to all in prior appropriation systems, and they often have an intrinsically sacred significance (Bryan, 2017). In contrast to state prior appropriation rights, they do not require diversion or consumptive use of water, which pose challenges for state water rights administration based on diversions and historical beneficial use (Nania and Guarino, 2014).

A second pivotal case in Montana in 1908, Winters v. United States (207 U.S. 564, 1908), determined that Indian reservations have reserved rights to the water necessary for their viability, which cannot be expropriated by later non-Indian users. Like federal reserved rights, Indian reserved rights date to the establishment of the reservation. Unlike other prior appropriation rights, however, their size is not based on the quantity of historical beneficial use. Tribal reserved rights affirmed in the lower Colorado River basin context of Arizona v. California (373 U.S. 546, 600, 1963) quantified them on the basis of “practicably irrigable acreage,” i.e., the amount of water required for potential vis-à-vis actual irrigation. That amounted to over 900,000 acre-feet in the Court's initial award to tribes along the lower Colorado River. The Supreme Court rejected Arizona's argument that tribal rights should be quantified on the basis “equitable apportionment,” as that principle applies at the interstate level, and Indian tribes are not states. These debates came up again in the Gila River context where the Arizona Supreme Court held that practicably irrigable acreage is one of several criteria to be used when quantifying Indian water rights (In re General Adjudication of All Rights to Use Water in the Gila River Sys. & Source, 201 Ariz. 307, 2001; cf. Hedden-Nicely, 2020).

Tribal water rights were further enmeshed in the multi-level system by the McCarren Amendment (43 U.S.C. 666, 1952) and U.S. Supreme Court case of Colorado River Water Conservation District v. United States, 424 U.S. 800 (1976), which stipulated that adjudication of Indian water rights must originate at the state court level, along with all other water rights in a state. The state level argument is that Indian water rights cannot be administered effectively unless they are part of a comprehensive state water rights adjudication. The counterarguments are that states do not have a trust responsibility for tribal interests, and that state water rights holders have an interest in constraining the size of Indian water rights.

A third category of Pueblo Indian rights, concentrated in New Mexico, dates to the Treaty of Guadalupe Hidalgo with Mexico in 1848 (art. VIII, 9 Stat. 922), which recognized the continuing validity of land and water rights in territory ceded to the United States at that time (Richard, 2017). The U.S. Supreme Court recognizing Pueblo Indian rights as aboriginal, i.e., prior to Hispanic rule (United States v Abouselman, 976 F.3d 1146, 1160, 2020). In contrast to Winters rights, however, historical water use is the basis for quantifying Pueblo Indian rights.

Subsequent Indian water rights cases have dealt with the implications of these precedents in various contexts, e.g., non-agricultural water uses, changes in water use, leases to locations off reservation lands, and to non-Indian allotment purchasers. A U.S. Bureau of Reclamation (2012) study estimated that adjudicated Indian water rights in the Colorado River basin currently amount to 2.9 million acre-feet (Getches-Wilkinson Center, 2021). Twelve tribes have quantifications that are pending. Ten are located in the lower basin, one in the upper basin, and the Navajo Nation has land in both halves of the basin. These unquantified, and quantified but undeveloped, Indian water rights pose uncertainties for users in the Colorado River system.

A number of inter-tribal initiatives address water concerns in the Colorado River basin. Five tribes have been involved in the Glen Canyon Dam Adaptive Management Program as it relates to the Grand Canyon ecosystem (Hopi, Hualapai, Navajo, Southern Paiute Consortium, and Zuni) (Jacobs and Wescoat, 2002). Every aspect of tribal involvement in this program, from representation to ways of expressing tribal views and processes of decision-making reflect the rich diversity of tribal water institutions (Hart, 1995; Roberts et al., 1995; Stoffle et al., 1995; Ferguson, 1998; Hualapai and Stevens, 1998; Shepherd, 2002; Austin et al., 2007; Seibert et al., 2007; Dongoske et al., 2010; Tribal Resources, 2022). In 1992, a Ten Tribes Partnership (2018) was organized to represent tribal interests and concerns. The Partnership prepared a water study with the Bureau of Reclamation that examines current tribal water rights, water uses, future development plans, challenges, opportunities, and potential effects in the basin. Tribes along the lower main stem (Colorado River Indian Tribes and Quechan tribe) have recently produced a series of videos titled, “One River, One Mission, One Voice: Protecting the Colorado River” to urge a new vision for basin stewardship (Ten Tribes Partnership., 2021). A Water and Tribes Initiative (Tanana et al., 2021) has prepared a report calling for Universal Access to Providing Clean Water for Tribes in the Colorado River Basin, which draws attention to longstanding deficiencies in safe domestic water supplies on reservations. These inter-tribal initiatives call for a different approach, one that encompasses and transcends historical institutional levels of water management in the basin—one that regards the river in some respects as a person, as sacred, and as alive—views considered in the discussion section below (Water Tribes Initiative, 2020).

As noted earlier, the United States acquired almost all of the Colorado River basin region from Mexico through the Treaty of Guadalupe Hidalgo (9 Stat. 922, 1848) and Gadsden Purchase (10 Stat. 1031, 1853-4), which established the international boundary. The treaty created a joint US and Mexico Boundary Survey (1857-59) that produced a three-volume report on the border region. In 1889 the two countries established an International Boundary and Water Commission/Comisión Internacional de Límites y Aguas (IBWC) to address alluvial changes in the international boundary and other mutual concerns.

The Colorado River Compact of 1922 and Boulder Canyon Project Act of 1928 anticipated a water treaty with Mexico at some point, which the states regarded as a federal obligation. Hundley (1966) reviewed the treaty negotiations in detail, highlighting the importance of their changing historical context. In early negotiations in 1927 Mexico sought 3.5 MAF per year while the U.S. offered 0.75 MAF. A decade later, Mexico sought 2 MAF while the U.S. offered 0.9 MAF. It is often reported that the negotiators incorrectly assumed that a total average annual yield of 19 MAF was available, though that is critically discussed by Kuhn and Fleck (2019). Finally, in 1944 for purposes of international comity during a time of war, the two countries concluded the Treaty on Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande (Department of State Treaty Series No. 994; 59 Stat. (Pt. 2) 1219, 1944). The U.S. wanted a treaty on the Rio Grande while Mexico wanted its share of the Colorado. In the Colorado River provisions, the treaty stipulates that the US. will deliver an average flow of 1.5 MAF per year, from any and all sources, with an additional 0.2 MAF in surplus years. The two countries agreed to make proportionate reductions during severe droughts, share flood protection costs, and coordinate through the IBWC (for critique of the latter see Mumme, 2005; McCarthy, 2011). The treaty was ratified in 1945, and as an agreement at the international level it takes precedence over policies at lower levels.

Soon after ratification Mexico relayed complaints about the salinity of water deliveries from the U.S. that caused agricultural damages. The U.S. began biennial salinity reports in 1965, and in 1973 the IBWC issued Minute 242 calling for the U.S. to establish salinity control standards and methods to ensure that the salinity of water delivered to Mexico would be no more than 115 ± 30 ppm greater than that of the water behind Imperial Dam (IBWC, 1973). That international level policy triggered a multi-level cascade of actions with federal, tribal, state, and community level implications across the basin. At the federal level, Congress passed the Colorado River Salinity Control Act of 1974 (Public Law 93–320 amended in 1984), which funded salinity control works below and above Imperial Dam. Upstream projects included water management improvements on local U.S. Bureau of Reclamation projects like the Grand Valley Project in western Colorado. That project co-financed improvements in irrigation efficiency to reduce groundwater leaching and brackish return flows–and it expressly did not alter irrigators' water rights held under Colorado water law.

Subsequent IBWC minutes have dealt with border sanitation at various localities, and with provision of emergency water deliveries to the city of Tijuana, the most recent in 2022. Concerns about severe and sustained drought arose in the 1950s, not long after the treaty was signed, and in subsequent droughts up to the present (Powell Consortium, 1995; Gangopadhyay et al., 2022).

At the start of the 21st century, the Colorado River basin region entered a multi-decadal megadrought that affects international treaty obligations and all levels of water management in the region. When the present drought became protracted, the U.S. Department of Interior (2007) developed “Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead.” As the drought continued for another decade, the IBWC (2017) issued Minute 323 on a “Binational Water Scarcity Contingency Plan,” to cover the period to 2026. Finally, in late 2021, the U.S. and Mexico negotiated a reduction of U.S. treaty obligations to Mexico (50,000 AF and 30,000 AF in recoverable savings) (IBWC, 2021); along with Tier 2 lower basin water reductions within the U.S. (330,000 and 200,000 AF in recoverable savings) in 2023, the first time since the treaty came into force in 1945, and it is not clear whether they will be sufficient.

Gleick (1988) undertook early investigations of potential international effects of global climate change on U.S. and Mexican water interests in the Colorado River. He and others extended that research to analyze impacts on international streamflow (Nash and Gleick, 1991) and environmental restoration flow requirements for the Colorado River delta in Mexico (Postel et al., 1998).

As at other levels, the international level has developed its own institutional rules, procedures, and organizations. They include the treaty-making power of the two nations, administrative role of the binational commission, and policy minutes that it negotiates on matters of mutual concern. As illustrated in recent salinity and drought issues, international deliberations are influenced by actors and arguments at all local and regional levels. And the resultant international agreements have implications that cascade through all institutional levels of water management (Conca, 2015; Rivera-Torres et al., 2021).