The paper presents an assessment of the state of water pollution of the Dzierzgoń Lake based on bacteriological indicators. Water samples were taken at two measurement points in four study periods in July and August 2011 and 2012. A total number of psychrophilic bacteria and MPN of faecal coliforms were determined. In addition, selected chemical parameters of water quality were analyzed, including total organic carbon and total nitrogen. The results were compared with those obtained by the Provincial Inspectorate for Environmental Protection in 1998 and 2004, and by Rychlik in 2009. It can be concluded that the sanitary condition of the Dzierzgoń Lake is satisfactory.