Msta River
Demyansky District is located in the Valdai Hills. As typical for the region, the east of the district contains many lakes. The biggest ones are Lake Seliger, which the district shares with Tver Oblast, and Lake Velyo, shared with Valdaysky District. Lake Seliger and adjacent areas belong to the basin of the Volga River. The western part of the district lies in the basin of the Pola River and its tributaries, the biggest of which are the Polomet and the Yavon. Minor areas in the east of the district belong to the drainage basin of the Msta River. The divide between the basins of the Atlantic Ocean (to which the Pola and the Msta belong) and the Caspian Sea (to which Lake Seliger belongs) thus runs through the district. 12% of the district's territory is occupied by the Valdaysky National Park, which protects forests and lakes in the Valdai Hills and includes Lake Seliger.