The Miho Dam (三保ダム, Miho damu) is a multi-purpose dam on the Kawauchi River, a tributary stream of the Sakawa River in the town of Yamakita, Ashigarakami District, Kanagawa Prefecture on the island of Honshū, Japan.

Development of the Sakawa River began in the 1960s, as a public works project to promote the local economies of towns in western Kanagawa prefecture.

Justification was provided by the projected growth in population of Odawara with the completion of the Tōkaidō Main Line railway and Tōmei Expressway and the continuing growth in demand from the Kawasaki-Yokohama industrial area for drinking and industrial water.

Work on the Miho Dam began in 1969 by the Kumagai Gumi construction company; and was completed in 1978.

The reservoir created by the dam, Lake Tanzawa is also a major recreational location for Kanagawa Prefecture.