Abstract
Studies on the influence of a perennial cormorant colony on chemical and microbial pollution of a reservoir were conducted in Chrzypskie Lake. During the investigation carried out between 2009–2010 in the area of the colony, 155–175 breeding pairs were observed. High pollution of groundwater with biogenic elements and coliform bacteria (together with E. coli) was recorded within the boundaries of the colony. Pollutants migrated to the lake together with groundwater. Mean values of the analyzed forms of biogenic elements and bacteria formed a gradient from the highest values recorded near the colony to the lowest ones recorded in the central part of the lake.