The Buyongwe River (French: Rivière Buyongwe) is a river in Burundi, a right tributary of the Akanyaru River.

The headwaters of the Buyongwe River are near those of the Nyamuswaga River. The Buyongwe forms in the west of Kirundo Province and flows southwest into Ngozi Province. It flows west past Kiremba, then southwest through marshes to the Akanyaru River. The Gisuma River is a left tributary of its lower reaches.

The surroundings of Buyongwe River are a mosaic of farmland and natural vegetation. They are densely populated, with 442 inhabitants per square kilometer. The average annual temperature in the area is 20 °C (68 °F). The warmest month is August, when the average temperature is 22 °C (72 °F), and the coldest is March, with 18 °C (64 °F). Average annual rainfall is 1,163 millimetres (45.8 in). The wettest month is March, with an average of 191 millimetres (7.5 in) of precipitation, and the driest is July, with 2 millimetres (0.079 in) of precipitation.

The area of the present Buyongwe marshes were dominated by Syzygium, Phoenix and Macaranga trees from 2700 and 1200 years ago. Then the trees began to disappear, possibly due to exploitation by Iron Age people, and there was an increase in aquatic plants that indicates a rising water table. Papyrus swamps began to develop 700 years ago.

Today, the Buyongwe marshes are surrounded by densely populated basins, and used to grow two crops of rice per year. A 2020 report noted that most of the rice mills or hullers given to agricultural cooperatives in Burundi operate only for a very short time, particularly for the cooperatives of the Buyongwe and Nyamabuno marshes.

• List of rivers of Burundi