The Pendjari River runs along the entire northern boundary of the park and gives both the park and the wider WAP complex their name. It is a seasonal river — heavy and silty in the rainy months, reduced to a string of long pools by April — and that retreat is exactly what makes the river country the prime game-viewing area of the park. As the surrounding bush dries out, elephant, buffalo, and the antelope herds concentrate on the remaining water, and the predators follow.
The northern park tracks run more or less parallel to the river, with several spots where the road drops down close to the banks. Look for hippos in the larger pools, crocodiles on the sandbars, and at dawn or dusk a high chance of large mammals coming down to drink. The Pendjari is the same watercourse known as the Oti further downstream where it crosses into Togo and Ghana before reaching the Volta basin — a small reminder that this corner of West Africa is more hydrologically connected than the political map suggests.