Mozhaysk Reservoir, Water reservoir in Moscow Oblast, Russia.

The Mozhaysk Reservoir is an artificial lake on the Moskva River in Moscow Oblast, formed in 1960–1962 by a dam and hydroelectric station near the village of Marfin Brod. It is about 47 km long and up to 3.5 km wide, with a surface area of 30.7 km² and a maximum depth of 22.5 m. The dam is 900 m long and carries a road with a checkpoint.

Planning began in 1948, when the Moscow City Executive Committee ordered a reservoir system on the Ruza and upper Moskva rivers to improve drinking water supply. Four dam layouts were studied to keep Borodino Field dry; the site stayed, and a dam and pumping station were built on the Koloch. The Moskva was dammed in January 1960 and the reservoir reached its design level in 1962.

Fishers and water sports enthusiasts regularly use the bays around the reservoir, especially on weekends and during warmer months. These activities shape the character of the shoreline and show how important the water body is to local recreation.

The dam and hydroelectric station stand near Marfin Brod, where a road crosses the 900-metre dam through a checkpoint. The reservoir freezes at the end of November and thaws at the end of April. In its upper part it becomes overgrown with reeds, and the Kolyoch River is pumped in over a protective dam.

The reservoir's dam near Marfin Brod carries a road with a controlled access system, and the reservoir was partially drained in 2008 and 2009 for repairs to the Mozhaysk hydroelectric station dams, lowering the water level by 6.5 m and 4.5 m below normal.