ABSTRACT
Berlin’s drinking water supply relies strongly on bank filtered water pumped from wells alongside its many lakes and rivers. One of these lakes, Lake Wannsee, shows hepatotoxic cyanobacterial blooms every year from July well into September. From September 2000 until Febuary 2002 water samples from observation wells situated in the adjacent aquifers were analyzed for their microcystin-content in order to verify whether bank filtration is an effective method to reduce cyanotoxins in raw water. The results show that during a cyanobacterial bloom only a very small amount of the total microcystin contained in the water body is recovered in the groundwater. There are, however, uncertainties about the fate of cyanobacterial cells that sink to the bottom of the lake and whether they can pose a long term threat to drinking water supplies.
