During 2004 and 2005 research on the malacocenoses existing in oxbow lakes differ in terms of hydrological connectivity was conducted in the valley of the Łyna River. The results showed that the connection of an oxbow lake with the river is the key factor influencing the abundance and biomass of molluscs in the lake. Three types of oxbow lakes representing lentic, semi-lotic and lotic environments were considered. In the lentic oxbow lake Mollusca was dominated by