Green Lake (6268)
Ethiopia, Africa

Site overview

KBA status: confirmed

Year of last assessment: 2011

National site name: Green Lake

Central coordinates: Latitude: 8.6960, Longitude: 38.9770

System: freshwater, terrestrial

Elevation (m): 1800 to 1900

Area of KBA (km²): 0.60187

KBA classification: Regional

Legacy site: Yes

Site details

Site description: Green Lake is one of a number of crater lakes near Debre Zeit in East Shewa Zone, 50 km west of the zonal capital, Nazaret. Like all of the volcanic crater lakes in this area, Green Lake is a closed system, being fed directly by rain and by water flowing down from the crater rims. The maximum depth is 32 m, and the water is highly alkaline. The lake is encircled by an almost continuous crater wall with steep and, in places, precipitous slopes rising almost 200 m above the water. Cliffs and scattered trees that grow on these cliffs make up the major habitats surrounding the lake. Drier slopes around the lake support various Acacia spp. where disturbance and grazing are minimal. Severely eroded areas are either bare or carry highly drought-tolerant shrubs, scramblers and succulents, the most conspicuous of which are Carissa edulis, Euphorbia tirucalli, Pterolobium stellatum, Caesalpina spinosa and Opuntia ficus-indica. The water exclusively supports an abundant population of the blue-green alga Spirulina platensis, as a result of which the water appears green (hence the name of the lake). The dense algal growth in the lake produces a huge amount of oxygen during the day, but at night photosynthesis ceases, the algae use up the oxygen, and the lake becomes almost completely anaerobic by daybreak. This phenomenon partly explains the absence of fish from the lake. Debre Zeit is an important town (see site ET032).

Rationale for qualifying as KBA: This site qualifies as a Key Biodiversity Area of international significance that was identified using previously established criteria and thresholds for the identification of Important Bird and Biodiversity Areas (IBAs) and for which available data indicate that it does not meet global KBA criteria and thresholds set out in the Global Standard. KBA identified in the process of compiling the CEPF Ecosystem Profile of the East Afromontane Hotspot. Species taxonomy and threat category was based on IUCN Red List 2010-4.

Additional biodiversity: See Box for key species. This lake is important for the large concentrations of waterfowl that it supports on a seasonal basis. Recent surveys have recorded c.80 species, including a range of Palearctic and Afrotropical waders, ducks and geese. Green Lake supports, along with the other Debre Zeit lakes, a wintering population of 10–15 Aythya nyroca. Of particular importance are the substantial numbers of Phoenicopterus minor known to use the lake: over 25,000 (including 2,000 dead birds) were recorded during a survey in November 1995, though a second survey in October 1996 found only 25. Other significant waterbird counts include Tachybaptus ruficollis (500 in 1995, 250 in 1996), Anas clypeata (700) and Himantopus himantopus (300). Non-bird biodiversity: None known to BirdLife International.

Delineation rationale: 2013-07-10 (BL Secretariat): following CEPF East Afromontane ecosystem profiling process, the reported IBA area of 54 ha has been changed to 60 ha (as measured in GIS from latest boundary polygon, rounded to nearest 10%).

Habitats

Land use: agriculture

Threats

Summary of threats to biodiversity at KBA: Increasing numbers of people and cattle from the surrounding area are using Green Lake, accelerating erosion and degradation of the crater’s steep slopes, and there is now excessive disturbance of the birds. There is also an increasing level of deliberate persecution of birds by local herdsmen, but whether this is responsible for the 2,000 dead Phoenicopterus minor noted in 1995 has not been confirmed. The dramatic decline in numbers of P. minor noted between 1995 and 1996, combined with the die-off noted above, is a serious cause for concern, and one that should be investigated to determine the cause. The local farmers would prefer to avoid the steep and treacherous descent to the lake for their cattle if alternative sources of water were available. During the rainy season they take their cattle to other watering points, away from the lake, suggesting that if there were an alternative watering-site for cattle, the farmers would not interfere with the wildlife of the Green Lake area.

Additional information