Makomanai Dam (Japanese: 真駒内ダム) is a rockfill dam located in Hokkaido Prefecture in Japan. The dam is used for irrigation. The catchment area of the dam is 49.5 km. The dam impounds about 56 ha of land when full and can store 6480 thousand cubic meters of water. The construction of the dam was started on 1965 and completed in 1986.