Lake Tana, largest lake of Ethiopia, in a depression of the northwest plateau, 6,000 feet (1,800 metres) above sea level. It forms the main reservoir for the Blue Nile (Abbay) River, which drains its southern extremity near Bahir Dar. Lake Tana was formed by volcanic activity, blocking the course of inflowing rivers in the early Pleistocene epoch, about 5 million years ago. Lake Tana has a number of islands, whose number varies depending on the level of the lake. Since there are no inflows that link the lake to other large waterways and the main outflow, the Blue Nile, is obstructed by the Blue Nile Falls, the lake supports a highly distinctive fish fauna, which generally is related to species from the Nile Basin.
