The Mangoky River is a 564-kilometer-long (350 mi) river in Madagascar. It rises in the Central Highlands of Madagascar just east of the city of Fianarantsoa. The river flows generally in a westerly direction out of the highlands, crosses the southern extension of the Bemaraha Plateau, reaches the coastal plain and its delta, and enters the Mozambique Channel north of the city of Morombe at .
Most of Madagascar has undergone serious deforestation during the last 40 years, which has led to extreme soil erosion in the Mangoky River basin, as evidenced by the many sandbars located within the river channel. Silt-laden, greenish-tan Lake Ihotry is clearly discernible south of the river. Between the lake and the coast is a rather large, whitish area of sand interspersed with silt-laden ponds. The southern portion of the delta is dominated by successive barrier island and spit formation. In contrast, the northern, protected portion of the delta is dominated by tidal passes and mangrove swamps.