Kaunas Reservoir (Lithuanian: Kauno marios, Kaunas Lagoon, Kaunas Sea) is the largest Lithuanian artificial lake, created in 1959 by damming the Nemunas River near Kaunas and Rumšiškės.
It occupies 63.5 square kilometers, which is about 0.1% of the total territory of Lithuania.
The reservoir supports the operations of the Kaunas Hydroelectric Power Plant. Its waters cover the Nemunas valley from the river’s confluence with Strėva River to the dam, a distance of about 25 kilometers. At its widest, the reservoir is 3.3 kilometers across and its greatest depth is 22 meters.
When the Nemunas was dammed in 1959-1960, the river water rose by 20 metres in 9 months, and at that time there were 35 villages and 700 homes in the flooded area of the lagoon, whose inhabitants were forcibly evicted by the Soviet government.
The reservoir also supports the operations of 900MW Kruonis Pumped Storage Plant, which is situated near confluence with Strėva River.
In 1992, in order to protect the local environment and cultural heritage, Kaunas Reservoir Regional Park was established. A yacht club operates in the park.
