Lake Seliger

|max-depth = Seliger (Селиге́р) is a lake in Ostashkovsky District of Tver Oblast and (in the extreme northern part) in Demyansky District of Novgorod Oblast of Russia, in the northwest of the Valdai Hills, a part of the Volga basin. It has an absolute height of 205 m, an area of 212 km2, and an average depth of 5.8 m.

Lake Seliger is a large system of bodies of water linked by channels, has many small islands, and is surrounded by forests - including pine woods with many berries and mushrooms. It is one of the biggest natural lakes of Central Russia. The only outflow of the lake, the Selizharovka River, flows from the southern end of the lake and drains into the Volga after 36 kilometres (22 mi). The drainage basin of the lake includes the major part of Ostashkovsky District, the south of Demyansky District, as well as minor areas in the Firovsky District of Tver Oblast.

Seliger is situated within a picturesque landscape of forests and hills. The lake is a protected nature reserve of the Tver Oblast () and "seasoned travellers" refer to it as the "European Baikal" |author-link1 = Vasily Peskov |publication-date = May 1979 |access-date = 17 February 2025 due to the diversity of its unique flora and fauna, similar to Lake Baikal. Valdaysky National Park covers the northern part of the lake.

Every year, Seliger camp forums bring together young people to study and discuss issues in political science, economics, art, literature and culture.

Ostashkov, the only town on the lake, is one of the most popular resorts in central Russia. The is located on Stolobny Island. The closed urban-type settlement of Solnechny, a military base, occupies Gorodomlya Island.