This reservoir was completed in 1965 by damming the Pangani river downstream of the confluence of the Ruvu and Kikuletwa rivers. The latter rises on Mount Meru to the north-west, collecting streams from Mount Kilimanjaro on its way. The Ruvu flows from Lake Jipe to the north-east and collects water from Mount Kilimanjaro and the Pare mountains. The surrounding habitat is dry Commiphora–Acacia woodland that slopes gently into the water. The lake is an important fishery and virtually the whole shoreline is utilized by fisherman who have established permanent settlements a few hundred metres from the water’s edge. The resultant shoreline is short grassland that becomes heavily overgrazed during the dry season. The northern shore, between the two rivers, is a seasonal swamp of considerable size, covering some 40 km² during the wet season. This swamp grades into an extensive woodland of mature Acacia xanthophloea that may hold an important heronry.
See Box and Table 3 for key species. Such a large source of fresh water in an otherwise dry environment is important to huge numbers of birds of many species. Many thousands of doves fly in to drink each day and there are often large mixed-species flocks of seed-eating passerines during the non-breeding season. The shoreline attracts large numbers of migrants, flocks of Charadrius asiaticus, Riparia riparia, Anthus cervinus and Motacilla flava are regular visitors and both Charadrius pecuarius and Vanellus spinosus occur in reasonable numbers. Although this lake is a freshwater habitat there are recent records of Charadrius pallidus, which suggests the habitat is facilitating the spread of this species away from its traditional alkaline sites in the Rift Valley. Maximum counts of Phoenicopterus minor have been of no more than a few thousand birds, but the site is probably of most importance during very dry years. Ardeola idae occurs and is probably a regular non-breeding visitor. The Ardea cinerea colony along the south-western shoreline is by far the largest known from East Africa. Over 1,500 Egretta garzetta have been recorded in January.The dry woodland holds populations of birds close to their southern limits such as Batis perkeo, Dryoscopus pringlii, Colius leucocephalus and Cosmopsarus regius. Along the Pangani river south of the dam there is a healthy population of Podica senegalensis, and Circaetus cinerascens probably breeds.
Non-bird biodiversity: None known to BirdLife International.
Pressure/threats to key biodiversity
The fishermen are tolerant of the birds and it is not unusual to see hundreds of egrets, herons, storks, Scopus umbretta and waders around the boats when a catch is being brought ashore. The swamp to the north is heavily utilized by the fishermen, but still appears to be an important breeding site for species such as Ardea purpurea and Ardeola ralloides. There is uncontrolled cutting of the Acacia woodland to the north of the swamp. Over-fishing is a potential threat. There are no known pollution problems and the state power company is likely to forbid uncontrolled expansion of the fishing villages.