Gorky Reservoir (Russian: Го́рьковское водохрани́лище), known colloquially as Gorky Sea (Russian: Го́рьковское мо́ре), is an artificial lake in the central part of the Volga River in Russia, formed by a hydroelectric dam of Gorky Hydroelectric Station (now called Nizhny Novgorod Hydroelectric Station) built in 1955 between the towns of Gorodets and Zavolzhye and filled in 1955 – 1957. It spans for 430 km from the dam of Rybinsk to the dam of Gorodets through Yaroslavl, Kostroma, Ivanovo and Nizhny Novgorod oblasts of Russia. While it is relatively narrow and follows the natural riverbed of Volga in the upper part, it becomes up to 16 km wide downstream the town of Yuryevets.
