Nishiyama Dam, Gravity dam in Hayakawa, Japan

Nishiyama Dam is a 40.4 m high concrete gravity dam on the Hayakawa in Naraida Shimokusori, Hayakawa, Yamanashi Prefecture. It is operated by the Yamanashi Prefectural Enterprise Bureau for hydropower and releases water through three emergency and one normal spillway gate. Its reservoir is named Narada Lake.

Nishiyama Dam began operating in April 1957, the first dam commissioned under the Norogawa Comprehensive Development promoted by Yamanashi governor Amano Hisashi under the slogan "Rich Yamanashi". It is a 40.4 m concrete gravity dam managed by the Yamanashi Prefectural Enterprise Bureau, and its reservoir is named Narada Lake.

The dam's reservoir is named Narada Lake, after the village of Narada in Hayakawa. Water from the Hayakawa and from the Narada No. 1 Power Station flows into it, and the lake's name is used locally for the stretch of water behind the dam. The dam is one of the first facilities completed under the Norogawa comprehensive development plan promoted by Yamanashi governor Hisashi Amano.

The dam stands in Naraida Shimokusori, Hayakawa, reached via the road along the Hayakawa River; the Nishiyama Power Station lies about 5 km downstream at Yushima on the river's right bank. Water is drawn from an intake on the lake's west side into a 4,906.9 m conduit, using a 147 m drop to turn the turbines. The dam has three emergency spillway gates and one normal spillway gate.

The reservoir behind the dam is named Narada Lake (Narada-ko). Water also reaches it from the Narada No. 1 Power Station, and the lake's water is drawn off on the west side into a 4,906.9 m conduit, using a 147 m drop to turn the turbines of Nishiyama Power Station about 5 km downstream in Yujima.