Masiwang River is a river of eastern Seram Island, Maluku province, Indonesia, about 2700 km northeast of the capital Jakarta.

[2] The Masiwang River flows through a wide valley, and is typically shallow, with a significant amount of sediment load.

[1] It flows into the sea on the southeast coast of Seram, between Tanjung Tioli, the eastern point of Waru Bay, and Tanjung Masiwang, forming a delta.

[5] The river flows in the eastern area of Seram island with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).

The warmest month is March, when the average temperature is around 24 °C, and the coldest is July, at 21 °C.