Once, the Common Waterbuck and the Defassa Waterbuck were considered two separate species.
Nowadays, modern taxonomists consider them as a single species. 
There are thirteen subspecies which are grouped under two varieties: the Common Waterbuck and the Defassa Waterbuck.
The distribution of the Common Waterbuck slightly overlaps that of the Defassa Waterbuck along the Rift Valley in Kenya, Tanzania and Zambia.

Kruger National Park, South Africa, 17 September 1997