The sampling sites in the lake were selected randomly according to the input of effluent from the watershed and other anthropogenic activities around the shoreline of the lake, as well as fish specimens from December 2010 to December 2020 including rainy and dry seasons. Six fixed stations (Figure 1) were used to collect water samples monthly. The choice of these areas was done according to fishermen who reported that they are mainly the potential fishing zones of the studied species (Bagrus bajad). The same sites also helped to collect specimens that helped for the reproduction and diet studies of the same fish species.

Each sampling area is described as follows: Drigi: is located in the South Bahema sector, at 500 m from the bank, receives waters from Drigi River, with an average depth of 4 m; aquatic macrophytes are dominated by Papyrus, Eicchornia, Fragmites spp; the bottom is sandy-muddy; the fauna is characterized by the presence of some individuals of hippos, sporadic crocodiles, turtles, possibly some

reptiles (snakes), and a diversity of aquatic birds. Human activity is exclusively dominated by cattle. Kicha ya Drigi: straddling the South Bahema sector (Irumu Territory) and the Bahema-Banywagi chiefdom (Djugu Territory); is located at 2 km from the bank, the bottom is sandy, a depth varying between 4 and 8 m; aquatic macrophytes appears during floods; Fauna is mostly dominated by aquatic birds); NJerere: belongs to the Bahema-Sud Sector, 1 km from Semliki delta, the sandy-muddy; the depth is 2 m average; the bottom is made of muds; aquatic macrophytes are dominated by Papyrus spp., Pennisetum spp., Eicchornia, etc.; fauna is composed of hippos, crocodiles, snakes and birds’ diversity. The villages surrounding the Semliki delta are populated by more than 3000 inhabitants. Human activities are mainly dominated by fishing. Songa Tabu (Rukwanzi): located on the border between the DRC and Uganda, from the Semliki delta, waters are loaded with organic matter; the average depth is 3 m; the vegetation is similar to that of Njerere; the bottom is sandy-muddy; the fauna is similar to that of Njerere; Inhabitants are currently estimated at more than 500 persons, other surrounding villages had been driven out by the floods that led migration either to Uganda or to Kasenyi and Tchomya (DRC). The most frequent human activities are exclusively fishing in the spawning area and small trade in these villages. Grand Bale: Bahema-South, located 2 km from the bank; sandy-muddy bottom, aquatic macrophytes vegetation are dominated by Papyrus, Eicchornia et Fragmites; the average melting is 3 m; there may be individuals of crocodiles, hippos, a diversity of birds, turtles etc.; human activities are exclusively dominated by fishing. Ingbokolo: belongs to Bahema-Sud sector, 4 km from the bank; the average depth is 4 m; the bottom is sandy; aquatic macrophytes vegetation is dominated Fragmites, Eicchorrnia; some birds are observed; limited human actions impact because the site is located far from villages.

To avoid contamination, non-powder vinyl clean gloves and masks were used during sample collection and laboratory work, and distilled deionized water was used for the analysis. The sterilized sampling bottles were rinsed with the lake water thrice before taking the original samples. All water samples were taken from a depth of ~15 cm from the water surface. The sampling bottles were labelled and transported to the laboratory. Until the laboratory analysis, all the samples were kept in the refrigerator at 4˚C (Mbalassa et al., 2014) [13].

The chemical parameters such as electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), dissolved oxygen (DO), major cations (Ca²⁺, Mg²⁺, K⁺, Na⁺, NH 4 + ), and the major anions (Cl⁻, NO 3 − , SO 4 2 − , PO 4 3 − , HCO 3 − ) were analyzed using the standard methods (APHA, 2005 [14]; Khadka et al., 2021 [4]). The pH, EC, and TDS were measured in the field using a multi-parameter instrument (HANNA). BOD₅ was measured as the decrease in DO after incubation in the dark at 20˚C for five days. The BOD₅ in mg/L of DO was calculated by subtracting the mg/L of DO in incubated sample bottles from the DO in initial bottles (Olompande et al., 2011) [15]. COD was calculated using potassium dichromate as an oxidant reagent (Bagalwa et al., 2006) [16]. Other water samples were taken in 1l plastic bottles at the same time, for other chemical analyses. The bottles were also rinsed thrice with sample water before final collection. The samples were placed in a cooler box with ice for transportation to the laboratory. If, analyses were not done immediately; samples had to be stored in a refrigerator at 4˚C. Hydro-carbonate ( HCO 3 − ) was estimateperimetricallyly using 0.1 N HCl wiphenolphthaleinein and bromocresol as indicators (5%). Total hardness was determined by complexometric method using EDTA after added a tampon and Eriochrome T indicator. Calcium also was determined by complexometric method using murexide indicators. Magnesium was determined by subtracting the Total hardness and calcium. The Chloride was determined by titration with silver nitrate and potassium chromate indicator (Golterman et al., 1978) [17]. The sulfate was determined using gravimetrical method. Fluoride was determined using a spectrophotometer (DR/2500 ODYSSEY at 650 nm). TSS (mg/l) were determined by filtration of 1l of water through analytical filter paper (Whatman 589, 185 μm pore size), which was dried at 105˚C and pre-weighed (APHA, 2005) [14]. The nutrients ( NO 2 − , NO 3 − , NH 4 + , TP and PO 4 3 − ) were determined using a spectrophotometer at 630 nm for nitrogen and 850 nm for phosphorus (Wetzel and Likens, 2000) [18]. The concentrations of Na⁺, F⁻, Fe⁺⁺ and K⁺ ions were determined by using Flame Photometer. Data were compared with UNECE (1994) [19] limit values of surface freshwater quality for the maintenance of aquatic life. Organic Pollution Index (OPI) were calculated based on BOD, nitrites, ammonium and phosphate (Gophen, 2012 [3]; Leclercq and Maquet, 1987; Mezbour et al., 2018).

Data analysis was done using Microsoft excel, the correlations between the parameters and different stations were done using PAlaeontological STatistics software (PAST). Results obtained were represented by use of text, graphs and statistical tables to show the interrelationships of various parameters in the stations.

A principal component analysis (PCA) was performed to evaluate the relationship between the sampling sites and the variation of the physicochemical parameters of the lake water. The resulting physicochemical parameters by sites were classified by cluster analysis (Ward’s method, Euclidean distance).

The pH was within the range of standard which indicates that the water is good for aquatic species (UNECE, 1994) [19]. The pH could be attributed to rocks in the study area that include the alkali-basalt, syenite and phonolites that have high concentration calcite minerals rich in carbonate ions (Hem, 1985) [24]. These variations are probably due to the input for watershed of runoff water coming from rivers as also observed by Olapade and Omotovin, (2012) [25] from Lake Kivu. Electrical conductivity is dependent on the type of rocks the

water is in contact with and how long it takes for water to percolate into the underground aquifer before to reach the lake (Lide, 1992) [26]. Water flowing in the Lake Albert basin tends to react with feldspath minerals mainly consisting of potassium, sodium and aluminum silicates before entering in the lake via rivers or groundwater (Wetzel, 2001) [27]. These tend to increase levels of dissolved ions in water (Hem, 1985) [24]. The low turbidity levels in underground water are attributed to the fact that silt sand and mud are trapped by the overlying rocks which act as a sieve. On the other hand, surface water had higher values of turbidity due to surface run-offs that carry silt and organic matter into the lake from streams and rivers (Karume et al., 2019 [23]; Muraga et al., 2017 [28]).

According to WHO drinking water guidelines, drinking water should have turbidity levels of below 5 NTU (WHO, 2006) [20]. The high levels of total dissolved solids (TDS) were attributed to the geology of the area of study that had high levels of sodium, calcium, carbonates and sulphates (Muraga et al., 2017) [28]. The standards require that water which is deemed safe for drinking should have TDS levels of less than 500 mg/L (UNECE, 1994) [19].

Generally, DO > 4 mg/L is suitable for drinking purposes and it was considered as 6 mg/L for the healthy aquatic life and metabolic activities of microorganisms (Pant and Adhikari, 2015) [29]. The direct diffusion from air and photosynthesis activity of autotrophs maintains the DO in water bodies (Pal et al., 2019).

Chloride levels in the Lake Albert surface water is between the standard acceptable limit of 250 mg/L (UNECE, 1994) [19]. The concentration of Cl⁻ in some sampling point could be due to anthropic activities like bathing, and others activities around the lake as found also by Khadka et al. (2021) [4] in Nepal. The Cl⁻ concentration in water is the indicator of anthropic disturbance and excessive chloride but this was not indicated in this study which can increase the level of TDS in water as observed by Pant et al., (2020) [30] in the Gandaki River, Central Himalaya Nepal. As also found in other lakes in the region as Lake Kivu and Lake Edward (Bagalwa et al., 2014 [31]; Karume et al., 2016 [32]; Bahaya et al., 2021 [33]). The fluoride levels were lower than those recommended by WHO of 1.5 ppm in water for human consumption (WHO, 2006) [20]. The Fluoride levels in the lake at these concentrations is essential in the formation of enamel in children, studies have shown that daily intake of fluoride at concentration above 0.5 mg/L could lead to mild dental fluorosis in children. The high levels of sulphates compared to different sites in surface water of Lake Albert could be attributed to anthropogenic activities and runoff from bedrocks. Whereas there is no known health risk associated with high intake of sulphates, it is recommended that drinking water should not exceed 500 mg/L of sulphate it would increase the risk of gastrointestinal effects such as diarrhea (WHO, 2006) [20].

Eutrophication is the major problem found in lakes due to phosphorous and nitrogen compounds. Their excessive concentration may lead to the growth of plants and algae and threaten the sustainability of the lake environment. Nitrates and Phosphates levels were lower at all the stations in the Lake. Concentration of nitrates and phosphates in surface water could be due to inorganic nitrate fertilizers or from contamination from human and animal wastes as a result of oxidation of ammonia by anaerobic bacteria and find their way in into waterways through surface run-offs (Bagalwa et al., 2015 [34]; Karume et al., 2016 [32]), the water indicating relatively moderate eutrophication as found also by Khadka et al., (2021) [4] in Jhilmila Lake, Kanchanpur, Nepal. The sources of PO 4 3 − in the lake water could be from the anthropic activities.

Most of the sampling sites showed total NH 4 + contents lie in permissible WHO guidelines. However, the NH 4 + contents were found comparatively more in some sampling points (t = 2.958; p < 0.05) in the lake could be due to sewage contaminations and natural degradation of organic matters, within the WHO guidelines for drinking water (<75 mg/L). Comparison of the physicochemical parameters of different sites was significative difference between them (F = 20.8; p < 0.05) mining that they have different water quality. This was also observed by Horsak et al., (2007) [35] on modern distribution patterns of snails and plants (Boukari et al., 2022) [36].

A principal component analysis (PCA) was carried out in order to highlight the relationships that may exist between the different parameters at the sampling points (Figure 5 and Figure 6). The factorial design summarized 74.47% of the overall information. The F1 axis, with 42.05% of the total variance is represented by Sodium, Potassium, Phosphate, Ammonium; Temperature, Turbidity, TSS, Conductivity, STD, CaH, Alkalinity, TH, MgH and pH. The groupings of these parameters in the two opposite poles of this axis show that the composition of the water is influenced by two different phenomena. The parameters salinity, conductivity and TDS provide information on the degree of mineral pollution of the water. There is an increasing mineralization gradient from the positive to the negative pole of the axis. The parameters temperature and SS determine the degree of organic pollution of the water. An increasing organic pollution gradient is created from the negative pole to the positive pole. Most of the information provided by the F2 axis (32.42% of variance) is explained by phosphorus, biological oxygen demand and dissolved oxygen (Figure 6).

Temperature shows a seasonal variation in wet season but no variation (p > 0.05) was recorded in dry season but is within the ranges UNECE, (1994) [19]. Temperature has a pronounced effect on the rate of chemical and biological processes in water; no other single factors affect development and growth of fish as much as water temperature (Babalola and Agbedi, 2013 [37]; Bagalwa et al., 2014 [31]; Odjohou et al., 2020 [38]). Based on the guideline of UNECE, (1994) [19], the pH of Lake Albert water has not adversely affected in aquatic ecosystem. This was also obtained in Lake Edward as recorded by Bagalwa et al., (2014) [31].

DO concentration in the lake is one of the important parameters in water quality assessment. It reflects the physical and biological processes prevailing in the water. High concentration of DO was recorded in wet and dry season compared to Lake Edward (Bagalwa et al., 2014 [31]; Ciwanine et al., 2020 [39]). The site Drigi has high DO levels during the period of sampling compared to other sites (p < 0.05). The site Ingbokolo has low DO compared to all other sites. Turbidity was high in Grand Bale in wet and Njerere and Kicha ya Digri in dry. According to Mbalassa et al., (2014) [13], transparency varied significative in Lake Edward as we recorded also in the Lake Albert during our sampling period. The turbidity affects the penetration of light underwater reduce the fish production, visibility but also the others biodiversity (Ali et al., 2000 [22]; Kamelan et al., 2022).

Nutrients are required to sustain life, but excess nutrient loads can upset the nutrient cycle balance resulting in changes in water quality harmful to organisms (Aldous et al., 2005) [40]. Nitrate and phosphorous concentration recorded in the water are washed from the basis of the lake as observed also in Lake Kivu (Bagalwa et al., 2015) [34]. There is a seasonal variation in some sites in the lake for the phosphorus and nitrate.

As most of African lakes at have been monimonitored, the concentration of physicochemical parameters is due to activities around their basin due to agriculture and urbanization. Lake Albert water quality is still pristine since concentration of phosphorus and nitrogen are not under the critical rates of eutrophication in the lake. The results suggest that although physicochemical parameters in these habitats were suitable for most aquatic species (UNECE, 1994 [19]; Soro et al., 2021 [41]) especially to Bargus bayad, they were subject to high spatial variations. The variations detected could reach adverse conditions if any measure is not taken to regulate agricultural activities in the basin of Lake Albert.