Most probable number (MPN) test was used to detect the presence of coliforms in sample water [15] . In presumptive MPN procedure, 15 lactose broth tubes were inoculated with the water samples. Five tubes received 10 ml of water, 5 tubes received 1 ml of water and 5 tubes received 0.1 ml of water. The number of tubes showing gas production and color change was compared to a standard table developed by American Public Health Association. The number of coliform was the MPN of coliforms per 100 ml of the water sample [16] .

The positive presumptive cultures were transferred to lactose broth, which is specific for fecal coliform bacteria. Any presumptive tube which showed gas production after 24 (±2) hours incubation at 44.5˚C (±0.2˚C), confirmed the presence of fecal coliform bacteria in that tube and was recorded as positive [17] .

To isolate specific pathogenic bacteria, the samples were enriched separately with alkaline peptone water (APW) for plating in thiosulfate citrate bile salts sucrose agar (TCBS) media, with GN (Gram-Negative) Broth for plating in Salmonella Shigella Agar (SS) agar, with Enterobacteria Enrichment Broth-Mossel for plating in MacConkey media. 1 ml of water from each sample was added with 3 ml of respective enrichment media. All the samples were then incubated at 37˚C for 24 hours. After overnight enrichment, the samples were plated in MacConkey, TCBS and SS agar plate separately. All the plates were incubated at 37˚C for 24 hours. After overnight incubation, the plates were observed for selective pathogens. For the confirmation of Escherichia coli, red/pink colonies form MacConkey agar plates were plated in eosin methylene blue agar (EMB) plates and for the confirmation of Vibrio cholerae and Vibrio parahaemolyticus, standard biochemical tests were performed from the yellow and green colonies in TCBS media respectively. Lactose fermenting (LF) and Non-LF bacteria were determined by differential media (MacConkey medium) to differentiate lactose fermenters (pink/yellow) colonies & non lactose fermenter colonies (colorless). Lastly, conformation of Shigella spp., Salmonella spp. and their serotype was determined with the antisera (polyvalent) developed by Denka Seiken, Japan [18] [19] .

Antibiotic susceptibility test was performed by disk diffusion method using the commercially available antibiotic disk on Mullar-Hinton agar to assess the susceptibility and resistance pattern of the isolates [20] . For this purpose, 12 different antibiotic discs were obtained from commercial sources (Himedia, India and Oxoid Ltd. England).

Cattle washing on public wetlands degrades water quality and sanctions concern microbial contaminants include fecal coliform and E. coli which are threatening to human and ecological health [21] . In our study, it was found that most of the water sample sources are not usually used for washing of cattle. Among twenty sample sources, one pond, two lakes and both rivers under study area were used for cattle washing activity by the people around it (Table 1).

At present, the majority number of water reservoirs in Bangladesh are unsafe for human due to dumping of domestic, untreated industrial and municipal wastes [22] . Most of our study areas were being used as a dumping point of waste. In this study, 55% (11 out of 20) of the sampling point was polluted by directly dumping of waste (Table 1).

The color of water is the important premier indicators of water quality which indicates its suitability for human, fishes or others inhabitants of water. Water should be clear and colorless for acceptance to the general public. Discoloration in water can be attributed to the presence of iron or magnesium or to the presence of humus, peat molecules, plankton and the pH level of the water. The WHO has established the color levels below 15 true color unit (TCU) are acceptable for most consumers and the color above 15 TCU are detected by naked eye [23] . The color of the investigated water sources was observed visually. Out of twenty sampling stations, three sampling point were deep green in color, seven points were light green in color, three point were gray in color, four point were turbid and other three water bodies were brown in color (Table 1). Water rich in phytoplankton and other algae usually appears green, soil runoff produces gray colors, dissolved organic matter, such as humus, peat or decaying plant matter can produce brown color and presence of much clay and unnecessary inorganic substances in water causes turbid color [24] .

The most people of rural village of Bangladesh use wetland water for their daily purposes (washing, cooking, bathing etc.) due to unavailable of safe water sources [4] . In our study, sample water of study area neither used for the drinking nor cooking purposes due to presence of available safe water sources. Most cases, these waters were used to take bath and Oju (for holiness of prayer) by the people living around it. But water of pond-8, pond-12, Lake-16 and Canal-18 even were not suitable for bathing and Oju too (Table 1).

Pure water (distilled) is odorless. The odor of the water indirectly indicates the severity of the pollution of water and the presence of toxic substances in it. The odor of the investigated sampling water was smelt by nose. About 85% of the sampling water had normal odor and 15% had bad odor during the June while 50% of the study point had bad odor during the February (Figure 2). Bad odor also results from discharging of domestic and industrial waste from the surrounding area and bacterial growth on water [25] .

pH is the vital factor of water which ensures the optimum environment for aquatic inhabitants. In our study, average pH values of the most of samples were more

than 7 which is slightly alkaline. This might be due to inorganic sediments or domestic and agricultural wastes disposed in it. The pH values of samples ranged from 7.12 - 8.51 (Figure 3). pH range (7.5 - 8.4) is good for the growth of algae and range (6.0 - 7.2) is optimum for laying fish [26] . As per STOAS, pH values 4 or less and 12 or high cause death to most of the fish species, 6 to 8 is the range for good growth and reproduction, and pH as low as 5 or as high as 9 to 11 do not allow fishes to reproduce as well as cause slow growth [27] . The observed values reflect its suitability for aquatic life.

Dissolved oxygen is essential for aquatic creature for respiration. Insufficient and imbalance DO may lead to cause of sudden death of these creature. In this study, values of DO at different sampling points were ranged from 2.8 to 6.1 mg/l. The highest DO value 6.1 mg/l was observed at two stations (pond-13 and lake-14) during June and the lowest DO 2.8 mg/l was also observed at pond-12 during February, which is not suitable for aquatic organisms (Figure 4). DO content should be above 6.0 mg/l for drinking water and more than 5.0 mg/l is suggested for fisheries, recreation and irrigation [28] . Except lake-14, all the sampling station had DO lower than 5 mg/l. during the February. Study showed that DO of the sampling station was not suitable for fish production during the

month of February.

According to the DoE standard, the ideal temperature of water for aquatic life is 20˚C to 30˚C [29] . The study showed that the range of temperature of all collected samples were (19.4˚C - 21.5˚C) during February and (27.7˚C - 29.8˚C) during June (Figure 5). The temperature range of June month fall within the DoE standard, but the temperature range of February month beneath the DoE standard. This is might be happened due to turbidity that prevent sunlight penetration, photo period which is directly related to the temperature, seasonality and flow rate.

Present study showed that all of the water samples contained a variety of bacteria. Total coliforms which are used to evaluate the general quality of water, exceeded the WHO recommended acceptable limit in all of our study sample [32] . The range of total coliforms in all of collected samples was varied from 1.9 × 10⁵ cfu/100ml to 6.3 × 10²³ cfu/100ml. The recorded mean concentration of total coliform was 4.5 × 10¹⁸ cfu/100ml during June and mean concentration was 4 × 10²² cfu/100ml during February (Figure 8). The coliform counts at several points of the Buriganga river water was varied from 1.1 × 10³ to 2.4 × 10³ cfu/100ml [33] . The maximum mean concentration of total coliform was 13.81

× 10²³cfu/100ml during May and minimum mean concentration of total coliform was 12.7 × 10⁸cfu/100ml during April in Dhaleshwari River, Tangail [19] . The underlying causes of maximum load of bacteria in February were unhygienic conditions besides the water bodies, less amount of water present and the less rainfall. On the other hand there were sufficient amount of water present due to heavy rainfall, increase the amount of water that reduce the concentration of bacteria during the June.

In our study, all of our samples were fecal coliform positive. Total coliform is a large collection of bacteria. Fecal coliform are types of total coliforms that exist in faeces. Fecal coliform bacteria are unlikely to cause illness, however their presence in drinking water may indicate the presence of disease-causing organisms [34] .

The count of E. coli in our collected samples exceeded the EPA’s recommended limit of E. coli [34] . E. coli is a subgroup of fecal coliform. The presence of E. coli in a drinking water sample usually indicates recent fecal contamination and means there is a greater risk that pathogens are present [35] . The range of E. coli in all of our collected samples was from 1.2 × 10³ cfu/100ml to 2.1 × 10¹² cfu/100ml. The recorded mean concentration of E. coli was 2.2 × 10⁷ cfu/100ml during February and mean concentration was 1.05 × 10¹¹ cfu/100ml during June (Figure 9). During June, monsoon rainwater runoff contaminated wetlands which causes the higher E. coli load in water.

Typhoid fever is a severe systemic infection which is triggered by the ingestion of the bacteria Salmonella typhi and Salmonella paratyphi. Transmission of this disease is linked to contaminated food and water or via contact with fecal matter from acute or chronically infected individuals [36] . Among 20 water bodies, only 5 were contaminated with Salmonella spp. in February (mean concentration

1.1 × 10⁵cfu/100ml) and 7 water bodies were contaminated in June (mean concentration 3.4 × 10⁵ cfu/100ml) (Figure 10). Among that contaminated water bodies, about 58% were contaminated with Salmonella typhi and 42% were contaminated with Salmonella paratyphi (Figure 11). Salmonella count in water showed peak during June and the prevalence of Salmonella typhi is higher than Salmonella paratyphi in Bangladesh [37] .

Vibrio cholerae caused cholera which is a major public health problem in developing countries like Bangladesh. Vibrio cholera is a waterborne pathogen and transmission of this bacteria is occurred through mainly contaminated aquatic sources or the faeces of an infected person [38] . Among 20 water bodies, only 8 were contaminated by Vibrio spp. in February (mean concentration 8.6 × 10⁵cfu/100ml) and 11 water bodies were contaminated in June (mean concentration 1.1 × 10⁸ cfu/100ml) (Figure 12). The ingestion of approximately 10⁴ - 10⁶ Vibrio cholerae organisms is likely to produce clinical cholera [39] . The load of Vibrio cholerae in our sample during both February and June are able to cause cholera outbreak. Among that contaminated water bodies, about 87% were contaminated by Vibrio cholerae and 13% were contaminated by Vibrio parahaemolytics (Figure 13). In Bangladesh, the outbreaks of cholera is mainly caused by Vibrio cholerae O139 and Vibrio cholerae o1 replaces the other with time in an endemic area or during a prolonged outbreak [40] .

Shigella spp. causes bacillary dysentery that can be transmitted by contaminated food and water. Research has shown a number of large waterborne outbreaks of shigellosis over the past years [41] . Among 20 water bodies, only 6 were contaminated with Shigella spp. in February (mean concentration 8 × 10⁴cfu/100ml) and 9 water bodies were contaminated in June (mean concentration 3.7 × 10⁷ cfu/100ml) (Figure 14). The load of Shigella spp. in study samples are enough to

cause shigellosis [42] . Among different serotypes of Shigella spp., Shigella dysenteriae were the dominating one. Among that contaminated water bodies, about 37% were contaminated by Shigella dysenteriae, 25% were contaminated by Shigella flexneri, 21% by Shigella sonnei and 17% by Shigella boydii (Figure 15). In Bangladesh two predominant Shigella spp., Shigella flexneri was isolated most frequently during August - January and Shigella dysenteriae during June to July [43] .