Lake Tana is the largest lake in Ethiopia and a source of the Blue Nile. It is located in Amhara Region in the north-western Ethiopian Highlands.
The Lake is located at an altitude of 1788 metres on the north central plateau of Amhara. 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).
With a surface area of 3,200 square kilometres but an average depth of only 14 metres due to high levels of sediment, Lake Tana is the largest single lake in Ethiopia and forms the main reservoir for the Blue Nile. 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. The lake was originally much larger than it is today.
Lake Tana from space
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Geography and Hydrology
Lake Tana is fed by the Gilgel Abay, Reb and Gumara rivers. The lake was known to the ancient Greeks as Pseboa or Koloe. Seven large permanent rivers feed the lake as well as 40 small seasonal rivers.
The alluvial Dembea plains on the lake’s northern shore and Fogera on the east indicate that the lake was at one time larger. The Blue Nile runs from Lake Tana's southeast corner, flowing south over a lava dam to form the Tisisat Falls - the name in Ethiopian means 'the water that smokes' - then flowing northwest to merge with the White Nile and form the full-fledged Nile itself.
The Blue Nile contributes two thirds of all the Nile discharge, along with most of the sediment carried along 4750 kilometres through to Egypt and the Mediterranean.
Because of the large seasonal variations in the inflow of its tributaries, rain and evaporation, the water levels of Lake Tana typically vary by 2-2.5 m (6.6-8.2 ft) in a year, peaking in September-October just after the main wet season.
Islands and Monasteries
Lake Tana has a number of islands, whose number varies depending on the level of the lake. It has fallen about 6 feet (1.8 m) in the last 400 years. Remains of ancient Ethiopian emperors and treasures of the Ethiopian Church are kept in the isolated island monasteries (including Kebran Gabriel, Ura Kidane Mehret, Narga Selassie, Daga Estifanos, Medhane Alem of Rema, Kota Maryam, and Mertola Maryam).
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These religious sites were created, in part, to protect Ethiopia's most valuable relics and treasures during times of war, according to the Earth Observatory. Dek's Narga Selassie monastery is one of several important religious sites scattered across the islands of Lake Tana.
On the island of Tana Qirqos is a rock shown to Paul B. Henze, on which he was told the Virgin Mary had rested on her journey back from Egypt; he was also told that Frumentius, who introduced Christianity to Ethiopia, is "allegedly buried on Tana Cherqos." Daga is arguably home to a more important monastery, named Daga Estifanos or "St.
The body of Yekuno Amlak is interred in the monastery of St. Stephen on Daga Island. Emperors whose tombs are also on Daga include Dawit I, Zara Yaqob, Za Dengel, and Fasilides. The monasteries are believed to have been built during the Middle Ages over earlier religious sites.
They include the fourteenth-century Debre Maryam, and the eighteenth-century Narga Selassie, Tana Qirqos (said to have housed the Ark of the Covenant before it was moved to Axum), and Ura Kidane Mehret, known for its regalia. There is also Zege Peninsula on the southwest portion of the lake.
Other major religious sites in Lake Tana include Tana Cherkos, an island populated exclusively by monks from the Ethiopian Church.
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Dek (center) and Daga (lower right) are two of the islands located within the milky green waters of Ethiopia's Lake Tana. In fact, the local "no females" rule is even applied to farm animals.
Dek and Daga Islands
Ecology and Biodiversity
Compared to other tropical lakes, the waters in Lake Tana are relatively cold, typically ranging from about 20 to 27 °C (68-81 °F). There are 27 fish species in Lake Tana and 20 of these are endemic. This includes one of only two known cyprinid species flocks (the other, from Lake Lanao in the Philippines, has been decimated by introduced species).
It consists of 15 relatively large, up to 1 m (3 ft 3 in) long, Labeobarbus barbs that formerly were included in Barbus instead. Their most important prey are the small Enteromius and Garra species.
In addition to the Labeobarbus species flock, the endemic species are Enteromius pleurogramma, E. tanapelagius, Garra regressus and Afronemacheilus abyssinicus (one of only two African stone loaches). The remaining non-endemic species are Nile tilapia (widespread in Africa, but with the endemic subspecies tana in the lake), E. humilis, G. dembecha, G.
Lake Tana also supports a subspecies of the Nile tilapia. Seventy percent of the lake’s fish populations are endemic to it, including cyprinids and African stone loach. Few invertebrates live in Lake Tana. There are few mollusk species that inhabit it, as well as a type of freshwater sponge.
Due to its immense size, the entire lake has been named Lake Tana Biosphere Reserve providing an important ecosystem which is a hotspot of biodiversity, and also has a global importance for agricultural genetic diversity.
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To the northeast of the lake is Simen Mountains National Park, a UNESCO World Heritage Site. These jagged mountain peaks and deep gorges are home to a number of rare animals including the Gelada baboon and Walia ibex, a type of goat.
Human Use and Threats
Lake Tana is used for fishing, farming and transportation, and has a thriving tourist industry centred on the more than 30 islands on the Lake, home to numerous Ethiopian Orthodox Church monasteries dating back more than five centuries. The lake region produces grains, oilseeds, and coffee. Cattle raising is important, as is fishing, carried on from the ancient tanqua (papyrus reed boat).
Lake Tana supports a large fishing industry, mainly based on the Labeobarbus barbs, Nile tilapia and sharptooth catfish. Other serious threats are habitat destruction and pollution. Bahir Dar has become a large city and it is rapidly growing; its wastewater is generally released directly into the lake.
The vegetation in the lake's wetlands, which are an important nursery for the Labeobarbus and other fish, are being cleared at a fast pace. A potentially serious threat to the unique ecosystem would be an introduction of a large and efficient predatory species like the Nile perch, which has been implicated in numerous extinctions in Lake Victoria.
Water for Africa’s Blue Nile River starts in Lake Tana, the largest lake in Ethiopia, sitting at 1,418 square miles. From there, it drains south. The Nile River is not as full as it once was, and neither is Lake Tana, whose water levels are controlled by a dam and hydro-power station.
| Feature | Description |
|---|---|
| Location | Amhara Region, Ethiopian Highlands |
| Surface Area | 3,000-3,500 km² (1,200-1,400 sq mi) |
| Max. Depth | 15 meters (49 feet) |
| Elevation | 1,788 meters (5,866 feet) |
| Primary Outflow | Blue Nile |
| Endemic Fish Species | 20 |
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