Lake Mantasoa is a large artificial lake with a surface area of 20.05 km2 (7.74 sq mi), created by the Mantasoa Dam on the Varahina river (an affluent of the Ikopa) in the municipality of Mantasoa, Analamanga region of Madagascar.

[1] It provides immediate irrigation for Betsimitatatra paddies in Analamanga and tabbed water for the capital Antananarivo.

The lake's lack of basal microfauna and ferruginous soil provides clear water.

[2] The area prior had been previously researched by Johann Maria Hildebrandt who collected fossils and fauna samples there in middle of 1880.

[3] It is home to one of only two sturgeon farms in the Southern Hemisphere beside the Rio Negro in Uruguay.