Tuesday, 28 February 2012 08:43

Lake Awassa

Written by  Fekade Daniel
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Lake Awassa ( 38o 25' East 7o 3' North ) covers an area of about 12900 ha and is situated at 1700 meters altitude. Lake Awassa lies to the west of Awassa town-275 km south of Addis Ababa.

The Awassa basin is in an old caldera in the middle of the Ethiopian Rift Valley, between the Abijata–Shalla basin to the north and that of Lakes Abaya and Chamo to the south. The walls of the caldera form steep walls to the north and east of the basin while most of the flatter areas are intensively cultivated. Lake Awassa is in the lowest portion of the caldera, along with a previously extensive wetland, Lake Shallo and the Shallo swamp. The swamp drains into Lake Awassa through a small river called Tiqur Wuha, which means ‘black water’.

There are no outlets from the lake, but water may seep away through the underlying volcanic ash and pumice. Awassa is a freshwater lake, even though the system appears to be closed. The level of the lake varies considerably from year to year and a dyke has been built to prevent the town from flooding.

The surface area ranges between 8,500 and 9,000 ha and the maximum depth is c.18–22 m. The shoreline varies between 50 and 65 km in length. Awassa is the smallest of the Rift Valley lakes, but is highly productive. It has a rich phytoplankton (over 100 species have been identified) and zooplankton that support large populations of six fish species. The most important commercial species is Oreochromis niloticus, but there are also good populations of catfish and Barbus.

The shoreline is gently sloping and mostly covered with vegetation that can extend 50 m or more into the lake. There are extensive beds of Cyperaceae and Typha spp. The dominant floating aquatic grass is Paspalidium geminatum, with other floating plants including Nymphaea coerulea, Pistia stratiotes and the smallest flowering plant in the world, Wolffia arrhiza. The lake supplies Awassa with all its water, and supports a thriving local fishery. The town and lake of Awassa form a popular resort for local and foreign visitors.

Birds of Lake Awassa

Significant numbers of congregatory waterbirds occur on the lake, with c.20,000 birds counted along less than 25% of the shoreline in January 1999. It is particularly important for Fulica cristata. Over 300 Leptoptilos crumeniferus (and 120 nests) were counted in November 1997, the largest concentration of this species in Ethiopia.

The population of this species (and of other waterbirds such as cormorants and pelicans) has risen steadily during the 1990s, probably due to the decline in fish populations in Lake Abijata .Other waterbirds occurring in good numbers include Alopochen aegyptiacus (1,464), Dendrocygna viduata (900), Plectropterus gambensis (712) and Threskiornis aethiopicus (311).

Other species of interest include Nettapus auritus, Ephippiorhynchus senegalensis, Circaetus cinereus, Falco ardosiaceus, Prodotiscus zambesiae, Centropus monachus, Salpornis spilonotus and Lagonosticta rubricata. Two Ethiopian endemics occur, Poicephalus flavifrons and Lybius undatus, along with at least seven Afrotropical Highlands biome species: Oriolus monacha, Lybius undatus, Nectarinia tacazze, Corvus crassirostris, Agapornis taranta, Passer swainsonii, Serinus citrinelloides and S. striolatus.

Key Species at Lake Awassa

Red-knobbed Coot (Fulica cristata) 
Giant King Fisher
Purple Swamp Hen 
Saddle Billed Stork 
Lesser Jacana

Last modified on Wednesday, 29 February 2012 07:02

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