From Wikipedia: http://en.wikipedia.org/wiki/Great_Ruaha_River

The Great Ruaha River is a river in south-central Tanzania that flows through the Usangu wetlands and the Ruaha National Park east into the Rufiji River. Its basin catchment area is 83,970 square kilometres (32,421 sq mi). The population of the basin is mainly sustained by irrigation and water-related livelihoods such as fishing and livestock keeping.