The Aswa river, a major tributary of the Nile, has its origins near Lake Kyoga, from which it is separated by a low watershed. The fishes described are the first to be collected from the Aswa. Two surprising features of the fish fauna are an endemic Synadontis species and an endemic and phyletically isolated species of Haplochromis. Despite the presence of several Nilotic species absent from the Kyoga-Victoria systems, the overall relationship of the Aswa species is with Lakes Victoria and Kyoga. It is suggested that the Aswa was once an affluent of Lake Kyoga.