Mantasoa Dam is a buttress dam on the Varahina-North River, a tributary of the Ikopa River, near Mantasoa in the Analamanga Region of Madagascar.

It creates Lake Mantasoa which has a surface area of 20 km2 (7.7 sq mi).

The dam itself is made of 8,000 m3 (10,000 cu yd) of concrete and has a reinforced buttress design.

[1] Water released from the dam supplies a regulated flow to hydroelectric power station at the Antelomita Dams downstream.

A saddle dam on the north side of the Mantosoa reservoir regulates water flow into the Mandraka River for the Mandraka Dam downstream.