Lake Tana is the largest lake in Ethiopia and the source of the Blue Nile. Located in Amhara Region in the north-western Ethiopian Highlands, the lake is approximately 84 kilometres (52 miles) long and 66 kilometres (41 miles) wide, with a maximum depth of 15 metres (49 feet), and an elevation of 1,788 metres (5,866 feet). Lake Tana is fed by the Gilgel Abay, Reb and Gumara rivers. Its surface area ranges from 3,000 to 3,500 square kilometres (1,200 to 1,400 square miles), depending on season and rainfall. The lake level has been regulated since the construction of the control weir where the lake discharges into the Blue Nile. This controls the flow to the Blue Nile Falls (Tis Abbai) and hydro-power station.
In 2015, the Lake Tana region was nominated as a UNESCO Biosphere Reserve recognizing its national and international natural and cultural importance.
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 aquatic fauna, which generally is related to species from the Nile Basin. The lake's nutrient levels are low.
Among other fauna, the lake supports relatively few invertebrates: There are fifteen species of molluscs, including one endemic, and also an endemic freshwater sponge.
About 230 species of birds, including more than 80 wetland birds such as the great white pelican, African darter, hamerkop, storks, African spoonbill, ibis, ducks, kingfishers and African fish eagle, are known from Lake Tana. It is an important resting and feeding ground for many Palearctic migrant waterbirds.
There are no crocodiles, but the African softshell turtle has been recorded near the Blue Nile outflow from the lake. Hippos are present, mostly near the Blue Nile outflow.