Lake Siriu is an artificial dam lake in Romania, on the Buzau river valley. Construction of the dam began in 1982, and the 42 MW Nehoiașu hydroelectric plant was opened in 1994. The dam is a 122 m high earthwork dam with a clay core, the second earthwork dam in Romania.

The purpose of the lake is to supply drinking and industrial water to the surrounding towns, plus irrigation of agricultural land.