The Kagera River, (also known as Alexandra Nile,) is an east African river, forming part of the upper headwaters of the Nile and carrying water from its most distant source.

The section of the river named Kagera begins in Burundi, flowing out from Lake Rweru. From the Lake, it flows east along the Rwanda-Burundi and Rwanda-Tanzania borders to a confluence with the Ruvubu River. The waters of the Kagera are thus provided by two major tributaries, the nyabarongo of Rwanda, which feeds Lake Rweru, and the Ruvubu of Burundi. It is unknown which of these two Feeder Rivers is the longer and hence the ultimate source of the Nile.

From the confluence, the Kagera flows north along the RwandaTanzania border, over Rusumo falls and through a Kagera national park. It then takes a turn to the east, following the TanzaniaUganda border and emptying into Lake Victoria in Uganda.

Kagera River has featured prominently in the histories of the countries it runs through, particularly Rwanda. In 1894, German Gustav Adolf von Gotzen crossed the Kagera at Rusumo falls, beginning the Rwandan colonial era; and in 1916, during World War I, the Belgians defeated the Germans, entering Rwanda by the same route. The river gained international notoriety in 1994 for carrying bodies from the Rwandan genocide into Lake Victoria, causing a state of emergency to be declared in areas of Uganda, where these bodies eventually washed up.

Kagera also rises in Burundi and flows into Lake Victoria. It is the largest single river into the Lake, contributing approximately 6.4 billion cubic meters of water a year (about 28 per cent of the Lake’s outflow). The Kagera is formed by the confluence of the Ruvuvu and the Nyabarongo, close to the northernmost point of Lake Tanganyika. It lends its name to a Kagera national park in northern Rwanda, as well as to the Kagera region of Tanzania. On the river are the Rusumo falls, an important crossing point between Rwanda and Tanzania. It is near the town of Rusumo.