The Mapi River or Mappi River (Indonesian: Sungai Mapi) is a river in South Papua, Indonesia.
The river flows in South Papua with a predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification). The annual average temperature in the area is 22 ðC. The warmest month is February when the average temperature is around 24 ðC, and the coldest is June, at 20 ðC. The average annual rainfall is 3143 mm. The wettest month is February, with an average of 403 mm rainfall, and the driest is July, with 66 mm rainfall. The average rainfall for the whole catchment area between 2002 and 2011 was 3577 mm.