The east beach strip of Lake Van is heavily populated and the place of wastewater discharges from a municipal refinery plant. To assess both the pollution rate and heterotrophic bacterial population in the lake water, samples were collected from 8 selected stations, 10 and 100 m far from the coast between the towns of Edremit and Zeve (approximately 20 km along the coast). Physico-chemical features (pH, temperature, dissolved 0,, biochemical 0, demand, suspended solid matter, total solid matter) of the lake have also been measured. Water samples were inoculated on starch casein agar supplemented with cycloheximide (50 mu g/ml) and nystatine (50 mu g/ml) to isolate actinomycetes, whereas nutrient agar and plate count agar technique were used to isolate the other microorganisms. The physico-chemical character of different water samples varied considerably. No actinomycetes were observed, but the total number of microorganisms was recorded to be 10(5) CFU ml(-1) in some water samples. The most diverse and active bacterial populations were found in the samples collected from the outlet of a wastewater treatment plant. Although a huge rate of organic matter flows into the lake, the water samples are polluted to a lesser degree owing to high soda content and high pH. Overall, the prokaryotic communities in the highly alkaline Lake Van represent an interesting new example of gram +/- bacteria well-adopted to a broad salinity range. But precaution should be taken into consideration as soon as possible to protect the east beach strip of Lake Van.