Drużno (Polish: Jezioro Druzno; German: Drausensee, Lithuanian: Drūsuo) is a body of water historically considered a lake in northern Poland on the east side of the Vistula delta, near the city of Elbląg. As it is currently not deep enough to qualify as a lake hydrologically and receives some periodic inflow of sea water from the Vistula Lagoon along the Elbląg River, some suggest that it be termed an estuary reservoir.