Piros

a lake in the Valdai Hills, on the border between Kalinin and Novgorod oblasts, RSFSR. It has an area of about 31.2 sq km and a maximum depth of 11.5 m. The lake is fed by mixed sources, chiefly snow. It freezes in late November or December and thaws in late April or May. The Berezaika River (Msta River basin) flows through Lake Piros, and a dam has been built where the Berezaika leaves the lake. The flow from Lake Piros is regulated to increase the flow and improve navigation on the Msta River.