It is the second largest lake in Poland, with an area of 104 square kilometres (40 sq mi).

It actually comprises six connected lakes: Mamry, Kirsajty, Kisajno, Dargin, Święcajty and Dobskie.

[1] Mamry features 33 islands, totaling 213 hectares (530 acres), some of which are ornithological reserves.

In the past, the lakes of the Mamry complex formed separate bodies of water connected by streams.

The following factors contributed to the rise of the water level in the Mamry complex: the dam on the Węgorapa River (the mill), movements of the earth crust - post-glacial rebound in the northern part of the complex by one millimetre (0.039 in) a year.