The field campaign started in October 2018 and lasted until February 2019. The water temperature and salinity and some of the physical/chemical parameters of the water were measured in the field using the CASTAWAY-CTD and Professional Plus Multiparameter Water Quality Professional Plus. Also, water samples were collected from eight locations in DB at five offshore locations and three outfalls (Figure 3 and Table 1). Samples from outfalls were collected during the low tide to avoid mixing the outfall discharge and the ambient seawater. The samples were collected using sterile plastic bottles of 1 L, stored in an icebox to limit biological and chemical activity, transported to the laboratory, and kept at 20 C. Unfortunately, it was impossible to obtain samples from the outfalls J1 and J2 and the area between the outfalls and the offshore due to safety concerns; the area is muddy, has soft beds, and is very shallow even at high tide was hard to reach by boat. J3 serves Saad Al-Abdallah residential area and Al-Jahra industrial area, J4 serves Sulaibiya Wastewater Treatment and Amghara industrial area, and J5 serves Jaber Al-Ahmad residential area (Figure 4). Water samples analysis was carried out at the National Unit of Environmental Research and Services (NURES) Project no–SRUL01/13, NUERS, Faculty of Science, Kuwait University. The pH, BOD, TSS, TDS, TOC, COD, nitrites, nitrates, ammonia, and phosphate were determined using the standard US EPA test methods (Nelson, 2003). The details of these tests are available through the US EPA website (https://www.epa.gov). In addition, the analysis of microbiological content (fecal coliform, E. coli) was carried out at KEPA laboratories. The isolation and numeration of microbial quality parameters (fecal coliform and E. coli) were conducted at each site for seawater samples to estimate the level of sewage contamination. This was undertaken using the membrane filter technique following the methods recommended by the Regional Organization for the Protection of the Marine Environment (Moopam, 2010) and Section 9222 D of Standard Methods for the Examination of Water and Wastewater (American Public Health Association (Apha), 1992). Under the aseptic technique, volumes 0.1, 1, 3, and 10 ml and serial dilution (10⁻¹, 10⁻³, and 10⁻⁵) using 0.1% peptone water for each seawater were filtered through sterile a 47-mm diameter, 0.45 μm pore size cellulose filter paper. Filter papers were then placed separately on m-FC media (EMD, Germany) with 10 ml 1% Rosolic acid in 0.2N NaOH, pH 7.4 plates. The plates were incubated at 44°C for 24 h. Counts were adjusted to the number of colonies per 100/ml of sample filtered (Lyons et al., 2015). The formula used to Counts the number of colonies per 100/ml of sample filtered is N o .   o f   b a c t e r i a / 100   m l = No .  of bacteria colonies  ×   100 The volume of the sample taken (1)

Finally, fecal streptococci were analyzed at MPW–Sanitary Engineering Sector–laboratories. Details of the laboratory analysis can be found in (Al-Nasser, 2022).

The statistical analysis and pollutant concentration mapping were conducted using SPSS and ArcGIS software. The statistical analysis includes DB water’s physical, chemical, and biological characteristics. The data of temperature, Acidity (pH), salinity, Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Total Organic Carbon (TOC), Biological Oxygen Demand (BOD), nitrate ( N O 3 − ), phosphorus, ammonia, and the microbiological indicators from the three outfalls and five offshore locations are included in the statistical analysis. In addition, all the data was compared to KEPA water quality standards and previous studies to assess the pollution level.

The concentration maps of E. coli, fecal coliform, and fecal Streptococci were done as follows:

1) The concentration map production was achieved using the Inverse Distance Weighted (IDW) interpolation method. The resulted map shows the concentration variation of the biological indicators spatially and temporally.

Table 4 summarizes the statistics of the water quality parameters from the J3, J4, and J5 outfalls, and Table 5 presents those of the offshore locations. The temperature differences between the three outfalls were negligible during the measurement times. However, the mean and maximum temperatures at the offshore locations (Table 5) were higher than those at the outfalls, while the minimum temperature was slightly lower. During all field campaigns, the temperature difference between the discharged water to the sea and the ambient seawater never exceeded 5°C, the maximum temperature difference allowed by KEPA (Table 2). The maximum temperature and salinity of 31.4°C and 43.9 PSU were recorded at D5 in September 2018. KEPA’s permanent stations near D5 show that the salinity and temperature vary between 41–44 PSU and 12–35.5°C over the year, respectively, and the peak values occurred in Septemper (Alkhalidi et al., 2021). It is necessary to mention that the higher salinity and temperature at D5 are due to its location offshore Doha power and Desalination plant, where numerous brine is discharged continuously (Nadi, 2015). Also, it is essential to mention that many fish kills incidents have occurred near this location over many years (Heil et al., 2001; Glibert et al., 2002; Islam and Tanaka, 2004; Piontkovski et al., 2012; Bacon et al., 2017; Alosairi and Alsulaiman, 2019; Alqattan and Gray, 2021). The fish kill incidents at high temperature and salinity locations confirm that high salinity and temperature are correlated with low Dissolved Oxygen (DO), as reported by Al-Yamani et al. (2004); Mann and Lazier (2013), and they directly affect marine fauna and flora and alter marine life.

The environment law of Kuwait requires that the pH level discharged to the sea must be between 6 and 9 (Kepa, 2014). The pH levels measured at the outfalls were within the allowable ranges of KEPA, with mean pH at outfalls J3, J4, and J5 being 7.5, 7.4, and 7.9, respectively. Inside DB, the maximum and mean pH values (Table 4) were slightly above the maximum seawater quality limit of KEPA (6.5 < pH < 8.5). The minimum and maximum pH values were recorded at D3 in December 2018. The mean pH values in DB are close to those reported by Al-Mutairi et al. (2014); Al-Sarawi et al. (2018). Al-Mutairi and others Al-Mutairi et al. (2014) relate the minimal variation in the pH levels to the high buffering capacity of KB.

The mean concentration of BOD at J3, J4, and J5 was 26, 11.6, and 3.3 mg/L, respectively. While the maximum recorded value of BOD was low at J5 (5.2 mg/L), it exceeds KEPA allowable limits (20 mg/L) six times at J3 (119 mg/L) and nearly two and half times at J4 (48 mg/L). Both maximum values at J3 and J5 were recorded in August 2018. Different studies (Al-Muzaini et al., 1991; Al Bakri and Kittaneh, 1998; El-Anbaawy et al., 2018) reported BOD levels in the range of 14–209 mg/L in SB (Figure 2), where many outfalls exist. The BOD and DO are inversely related, and hence in addition to the impact of high temperature, salinity, and evaporation rates, discharging pollutants with these high levels of BOD into DB and KB contribute significantly to the deterioration of the environmental status of the bay, the diversity of species, and the fish stock decline (Martina and Radjawane, 2019; Alqattan and Gray, 2021).

The mean TSS concentration at J3 was excessively high, with maximum, minimum, and mean values of 2184, 88, and 547 mg/L, respectively. The maximum concentration recorded was 2184 mg/L in October 2018. Knowing that the maximum concentration level allowed from KEPA to be discharged to the sea is 10 mg/L, the amount of TSS disposed to the sea from J3 is unacceptable and contributes to the bay’s environmental deterioration. The mean concentrations of TSS at J4 and J5 were 23 and 16.4 mg/L, respectively, while the maximum values were 72 and 26 mg/L. These levels are also above KEPA maximum limits but much lower than J3. Offshore the mean TSS concentration was 10.16 mg/L, with a maximum value of 30 mg/L at D1 recorded in September 2018 and a minimum value of 2 mg/L at D5 recorded in December 2018. KEPA’s maximum allowed value for TSS in the coastal water of Kuwait is 30 mg/L. In KB, the mean concentration of TSS is 14.1 mg/L, with a maximum of 29.1 mg/L (Al-Mutairi et al., 2014). Comparing the TSS values inside the bay with those outside the bay, the bay’s high TSS is due to sewage discharge and the shallowness of the western part of the bay (Devlin et al., 2015). Other factors of high TSS are the Shamal wind, rainstorms, and the bay’s slow flushing (Devlin et al., 2019). These factors also elevate the turbidity values in winter (Devlin et al., 2019). Since D5 is located at the DB entrance (the faster water flushing, larger tidal currents, and deeper water), TSS is significantly lower than the other offshore stations. KEPA’s stations Z02 recorded a mean and maximum concentration of TSS of 17.2 and 985 mg/L, respectively.

The maximum concentrations of TDS in Table 4 were all measured in August 2018. A maximum concentration of 8328 mg/L was measured at J5, and the minimum, 708 mg/L, was measured at J4 in December 2018. Dashti and Al-Haddad (2019), in April and May 2019, found higher TDS concentrations near the outfalls of SB. The range of TDS in their sampling campaign was between 31,747 mg/L and 44,270 mg/L. Al Bakri and Kittaneh (1998) classified DB as a slightly polluted embayment with TDS. High TDS concentrations are expected in such embayment due to natural and human stressors such as extreme climate and excessive waste discharge.

On the other hand, the TOC levels at the outfalls and offshore were lower than KEPA maximum limits. For example, KEPA requires that TOC concentration discharged to the sea not exceed 40 mg/L while the maximum concentration measured was 25.8 mg/L at J3 in December 2018. These measurements contradict many studies that reported high levels of TOC in KB in general. Al-Said and others Al-Said et al. (2018) conducted a two-year water sampling campaign to assess the TOC of Kuwait’s territorial coastal water from 2014 to 2016. Their findings showed that high TOC levels in Kuwait’s coastal water are the highest measured in any marine system. Also, they reported that these TOC levels are maximum in DB and decrease offshore and toward the open water. Two leading contributors increase the TOC levels in seawater. These contributors are the waste discharge and the high salinity due to the brine discharge, making the seawater denser. The discrepancy between the TOC of this study and (Al-Said et al., 2018) requires establishing a monitoring program for Doha Bay due to its environmental sensitivity and importance and because it is considered the most polluted area in Kuwaiti regional waters.

KEPA allows water to be discharged to the sea with a COD level of not more than 100 mg/L Kepa (2014). The data of this study show that the mean COD concentrations exiting J3 and J4 outfalls are 226 and 105 mg/L, respectively. The mean and maximum COD concentrations existing from J5 were 39.7 and 96, respectively, below the KEPA maximum limit, while the maximum COD level was measured at J3 at a value of 518 mg/L in August 2018. The second highest values were recorded at J4 with a maximum value of 201 mg/L in August 2018. Seater samples collected from SB by El-Anbaawy et al. (2018) show high levels of COD in the range of 94.3 and 120 mg/L. The high levels of COD deplete the oxygen demand in the seawater and hence directly affect the environment and marine life.

Nitrites ( N O 2 − ) are produced from wastewater treatment and desalination plants. The mean The data from outfalls J4 and J5 shows negligible levels of NO₂. On the other hand, the NO₂ at J3 was significantly high, with a mean value of 29.8 μg/L and a maximum value of 89.4 μg/L measured in October 2018. Still, the mean NO₂ concentration in DB was 0.23 μg/L, and the maximum was 0.6 μg/L, which is significantly lower than the KEPA seawater quality maximum value for NO₂, 35 μg/L. DB’s nitrate ( N O 3 − ) levels were negligible compared to KEPA seawater quality maximum value for NO₃, 95 μg/L.

Phosphate ( P O 4   3 − ) concentrations were within KEPA seawater quality maximum value for PO₄, 34 μg/L, at the outfalls and offshore. The maximum concentration from the outfalls was 4.8 μg/L recorded at J3, and the maximum offshore concentration was 0.3 μg/l. A high concentration of PO₄ (>1000 μg/L) was recorded by KEAP and the ministry of Public Works in 2009 in KB due to the Mishref pumping station breakdown and discharging of raw sewage directly to the sea.

The mean concentration of ammonia (NH₃) in J3 and J4 was 17.2 and 15 μg/L, respectively, and there was no NH₃ measurement at J5. The maximum concentration of NH₃ was 28.9 μg/L measured at J3 and was 18.2 μg/L at J4. These values exceeded KEPA’s maximum allowable NH₃ to be discharged to the sea, 1 μg/L.

Microbiological pollution near coastal areas is hazardous to beach users because feces may contain pathogenic microorganisms that can be ingested and bring intestinal problems (Lee et al., 2002; Lee, 2006). Studies and Epidemiological surveys revealed a positive correlation between fecal pollution in coastal areas and swimming diseases (Wade et al., 2003). KEPA seawater quality guidelines of bacterial indicators in water discharge through coastal outfalls are 500 CFU/100 ml for fecal coliform bacteria, 500 CFU/100 ml for Escherichia coli, and 200 CFU/100 ml for fecal streptococci bacteria. During the field campaign of this study, samples and measurements were taken from the three outfalls (J3, J4, and J5) and offshore locations (D1—D5). It was noticed that the sewage discharge from J5 was minimal compared to J3 and J4, and there was no continuous raw sewage discharge to the sea from J5. Table 6 summarizes the microbial water quality indicators at the outfalls. Figure 5 presents the spatial and temporal variations of the microbiological water quality indicators. Table 6 and Figure 5 show extremely high fecal coliform and E. coli at all outfalls and offshore locations, specifically during January and February 2019 (Figures 6, 7). The minimum E. coli concentration was 5 × 10² CFU/100ml, the maximum limit concentration allowed by KEPA (discharged from J5 in December 2018). The mean concentration of E. coli from J3 is nearly 18 and 86 times that from J4 and J5, respectively. fecal Streptococci concentration levels discharged from the J5 outfall were consistently below the KEPA maximum allowed limit, but at J3 and J4, the mean levels exceeded KEPA maximum limits by 3.65 and 2.2 times, respectively. The maximum level of fecal coliform varies between 1 × 10⁴ and 3.5 × 10⁵ CFU/100 ml at J5 and J3, respectively. These levels are exceeding the KEPA maximum limits significantly. The minimum levels of fecal coliform were between 2.5 × 10³ and 3 × 10⁵ CFU/100 ml at J4 and J3, respectively. These levels are also high, exceeding KEPA limits, and indicating the beaches of DB can be considered a health hazard location for swimmers and the health of the bay’s fish consumers.

Figures 6–8 show the maximum concentration of the microbiological indicators in DB using ArcGIS. The figures show the highest concentration was in the west area of DB, around D1 and D2, and the lowest concentration was around J5 and D3. The concentration around D4 and D5 was higher than around D3 due to the waste discharge from SB (north-south of D4 and D5). The concentration of the extreme values near D1 and D2 because they are very close to the outfall J3, which discharges more pollutants to the bay than the other outfalls (Figures 6–8).

The results in Table 6 confirm the claim of Aleisa and Al-Shayji (2019) that 88.89 million m³/year of wastewater remains untreated and discharged to the sea. In addition, Lyons et al. (2015) indicated that illegal connections to the storm drains are responsible for the sewage pollution in DB.

Figure 5 shows that DB is highly polluted with microbiological indicators, and this pollution is mainly due to the continuous sewage discharge from the three outfalls, specifically from J3. Locations D1 and D2 are significantly more polluted than D3, D4, and D5. This significant more pollution at D1 and D2 is because these two locations are closer to outfalls J3 and J4 and are in shallower water depths than the other locations. Saeed and others Saeed et al. (2015) reported that most of the southern part of KB is highly polluted with fecal.