Lake district, northeastern Poland, containing more than 2,000 lakes.
It extends 180 mi (290 km) eastward from the lower Vistula River to the Poland-Belarus border and occupies an area of 20,000 sq mi (52,000 sq km). It was the scene of Russian defeats in 1914–15 during World War I. It came under Russian control in January 1945 but was later granted to Poland by the Potsdam Conference .