Local boatmen can take visitors by pirogue into the channels and backwaters around Ayorou, where hippos are sometimes seen. Nothing is guaranteed, and the trip is at its best when treated as a river outing rather than a safari: low banks, reed beds, fishing boats, and the slow rhythm of travel by water.
Ask around at the riverfront or through your driver, agree the price before leaving, and do not push boatmen to get too close to hippos. They are powerful, unpredictable animals, and the best view is from a respectful distance.