The Masurian Lake District (Polish: Pojezierze Mazurskie, German: Masurische Seenplatte) is a lake district in northeastern Poland containing more than 2,000 lakes.
It extends roughly 290 km (180 mi) eastwards from the lower Vistula River to the Poland-Lithuania border and occupies an area of roughly 52,000 km² (20,000 sq mi). Administratively, the lake district lies within the Warmian-Masurian Voivodeship. (From the 13th century until 1945, it was part of East Prussia). Small parts of the district lie within the Masovian and Podlachian Voivodeships.
The lake district was shaped by the Pleistocene ice age. Many of its hills are parts of moraines and many of its lakes are moraine-dammed lakes.