a group of lakes in northeastern Poland, located in the central part of the Masurian Lake Region. The lakes, usually occupying intermoraine depressions, have a total area of 310 sq km; the largest lakes are Sniardwy (113.8 sq km) and Mamry (104 sq km). Their maximum depth is 40 m (Lakes Mamry and Niegocin). The Masurian Lakes form a chain of inland water bodies linked by streams and canals. They flow into the Vistula and Pregel basins.
The lakes are used for sailing and fishing, chiefly zander, eels, and pike; they abound in waterfowl. There are sanatoriums along the shores, and the area is a popular tourist spot. During World War I the region was the site of bloody battles between the Russian and German armies in 1914-15.