[2] Its altitude ranges between 1,000 and 1,100 m (3,300 and 3,600 ft), dominated by the Acacia-Commiphora bushland on the north shore of Kamburu Reservoir, at the confluence of Tana and Thiba Rivers.

Open grasslands are dominant along the main rivers, with occasional thick undergrowth, as well as a riparian or riverine woodland.

Game species range from African elephants, lesser kudus, Nile crocodiles, giraffes, Grant's zebras, buffalos, African leopards, common duikers, black-backed jackals, bushbucks, waterbucks, Sykes' monkeys, warthogs, rock hyraxes, bush pigs, impalas and hartebeests.

The reserve is the only protected area in which the globally threatened and Kenya-endemic Hinde's babbler (Turdoides hindei) is known to occur.

Mwea National Reserve also shelters two other rare species; the Pel's fishing owl (Scotopelia peli) and the white-backed night heron (Gorsachius leuconotus).