Lake Tana

Coordinates: 12°0′N 37°15′E / 12.000°N 37.250°E / 12.000; 37.250
Source: Wikipedia, the free encyclopedia.
Lake Tana
Primary inflows
Gilgel Abay, Kilti River, Magech River, Reb River, Gumara River
Primary outflowsBlue Nile
Basin countriesEthiopia
Max. length84 km (52 mi)
Max. width66 km (41 mi)
Surface area3,200 km2 (1,200 sq mi)
Max. depth15 m (49 ft)
Surface elevation1,788 m (5,866 ft)
IslandsThe most important are Tana Qirqos, Daga Island, Dek Island, and Mitraha
SettlementsBahir Dar, Gorgora

Lake Tana (

romanized: T’ana ḥāyik’i; previously Tsana[1]) is the largest lake in Ethiopia and a 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),[2] and an elevation of 1,788 metres (5,866 feet).[3] 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.[4]

Overview

Views over Lake Tana
The Island Church on Lake Tana
A local tour guide demonstrates how a stone is struck to signal meal times at a monastery on Zege Peninsula
Beginning of the Blue Nile river by its outlet from Lake Tana
A resort hotel on Lake Tana in 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.[5]

The lake was originally much larger than it is today. Seven large permanent rivers feed the lake as well as 40 small seasonal rivers. The main tributaries to the lake are Gilgel Abbay (Little Nile River), and the Megech, Gumara, and Rib rivers.[5]

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. According to

Manoel de Almeida (a Portuguese missionary in the early 17th century), there were 21 islands, seven to eight of which had monasteries on them "formerly large, but now much diminished."[6] When James Bruce visited the area in 1771, he noted that the locals counted 45 inhabited islands, but stated he believed that "the number may be about eleven."[6] Anton Stecker, in 1881, made a detailed examination of the lake, enabling substantially accurate maps,[1] and counted 44 islands.[7] A 20th-century geographer named 37 islands, of which he believed 19 have or had monasteries or churches on them.[6]

Remains of ancient Ethiopian emperors and treasures of the

Fasilides. Other important islands in Lake Tana include Dek, Mitraha, Gelila Zakarias, Halimun and Briguida
.

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. A ferry service links Bahir Dar with Gorgora via Dek Island and various lakeshore villages.

There is also Zege Peninsula on the southwest portion of the lake. Zege is the site of the Azwa Maryam monastery.

Water characteristics and floods

Compared to other tropical lakes, the waters in Lake Tana are relatively cold, typically ranging from about 20 to 27 °C (68–81 °F). The water has a

alkaline and its transparency is quite low.[9]

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. When the water levels are high, the plains around the lake often are flooded and other permanent swamps in the region become connected to the lake.[9]

Fauna

Lily pads floating near the shore on Lake Tana

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.[10] The lake's nutrient levels are low.[9]

Fish

There are 27 fish species in Lake Tana and 20 of these are

chironomid larvae. Among the endemic Labeobarbus, eight species spawn in the lake's wetlands and the remaining move seasonally into its tributaries where they spawn.[9]

In addition to the Labeobarbus species flock, the endemic species are

African sharptooth catfish.[9][10]

Fishing and threats

African sharptooth catfish
caught in the lake

Lake Tana supports a large

IUCN.[14] In the early 2000s, the local government for the first time introduced a fisheries legislation and it is hoped this will have a positive effect on the fish populations.[9]

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.[9] 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. The piscivorous Labeobarbus of Lake Tana are relatively inefficient predators that can only take fish up to about 15% of the length of the predator itself.[9]

Other fauna

Great white pelicans on Lake Tana

Among other fauna, the lake supports relatively few invertebrates: There are fifteen species of

mollusks, including one endemic, and also an endemic freshwater sponge.[10]

About 230 species of birds, including more than 80 wetland birds such as the

Palearctic migrant waterbirds.[10]

There are no

Hippos are present, mostly near the Blue Nile outflow.[9]

References

  1. ^ a b Garstin & Cana 1911.
  2. ^ Statistical Abstract of Ethiopia. 1967–68.
  3. ^ "Lake Tana, source of the Blue Nile". Observing the Earth. European Space Agency. 5 November 2004. Retrieved 4 November 2013.
  4. ^ Homepage of Lake Tana Biosphere Reserve
  5. ^
    ISBN 978-1-4020-9725-6
    .
  6. ^ a b c C.F. Beckham and G.W.B. Huntingford, Some Records of Ethiopia, 1593-1646, (series 2, no. 107; London: Hakluyt Society, 1954), p. 35 and note.
  7. ^ Hayes, A.J. (1905). The Source of the Blue Nile: A Record of a Journey Through the Soudan to Lake Tsana in Western Abyssinia, and of the Return to Egypt by the Valley of the Atbara. Smith, Elder & Company. p. 73. Retrieved 2021-05-28.
  8. ISBN 978-0312227197
  9. ^
    ISBN 978-1-4020-9725-6
    .
  10. ^ a b c d e Freshwater Ecoregions of the World (2008). Lake Tana. Archived 2011-10-05 at the Wayback Machine Accessed 24 January 2012
  11. ^ a b de Graaf, Dejen, Sibbing and Osse (2000). Barbus tanapelagius, A New Species from Lake Tana (Ethiopia): its Morphology and Ecology. Environmental Biology of Fishes 59 (1): 1-9.
  12. ^ de Graaf, Megens, Samallo, Sibbing (2007). Evolutionary origin of Lake Tana's (Ethiopia) small Barbus species: indications of rapid ecological divergence and speciation. Animal Biology 57(1): 39-48.
  13. ^ "Information on Fisheries Management in the Federal Democratic Republic of Ethiopia", Food and Agricultural Organization (FAO), January 2003
  14. ^ "The IUCN Red List of Threatened Species". IUCN. 2019. Retrieved 18 November 2019.
  15. ISBN 978-3-89973-466-9

External links

Wikimedia Commons has media related to Lake Tana.
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