The Southern Ewaso Ng'iro (Brown River) is a river in the

Great Rift Valley The Great Rift Valley is a series of contiguous geographic trenches, approximately in total length, that runs from Lebanon in Asia to Mozambique in Southeast Africa. While the name continues in some usages, it is rarely used in geology as it i ...

Kenya ) , national_anthem = "Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

. It plays an important role in the ecology of

Lake Natron Lake Natron is a salt or alkaline lake located in north Ngorongoro District of Arusha Region in Tanzania. It is in the Gregory Rift, which is the eastern branch of the East African Rift. The lake is within the Lake Natron Basin, a Ramsar Site ...

, the main regular breeding site for near-threatened

lesser flamingo The lesser flamingo (''Phoeniconaias minor'') is a species of flamingo occurring in sub-Saharan Africa and western India. Birds are occasionally reported from further north, but these are generally considered Vagrancy (biology), vagrants. Charac ...

s. Changes to land use in the river's headwaters or in the marshes before the river enters the lake could have a serious impact on this species.

Course

The Ewaso Ng'iro rises on the

Mau Escarpment The Mau Escarpment is a fault scarp running along the western edge of the Great Rift Valley in Kenya. The top of the escarpment reaches approximately 3000 m (10,000 ft) above sea level, and is over 1000 m higher than the floor of the ...

, where it drains the south part of the

Mau Forest Mau Forest is a forest complex in the Rift Valley of Kenya. It is the largest indigenous montane forest in East Africa. The Mau Forest complex has an area of . The forest area has some of the highest rainfall rates in Kenya. Mau Forest is the la ...

. The forest, which plays an important role in regulating and filtering the inflow to the river, is under threat from logging and land clearance for farming. Destruction would increase sediment loads in the river and cause greater seasonal variance in the volume of water. The river flows south through the rift valley to the east of the

Nguruman Escarpment Nguruman Escarpment is an escarpment in southern Kenya. The escarpment is around 50 kilometres long and elongated in N-W direction. Its northern edge approximately 120 km southwest of Nairobi, while the southern edge is near the Tanzanian bord ...

. It crosses the border into

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...

, where it empties into

. The river, which runs all year round, is the main inflow to the lake. The river once flowed directly into the lake, but in geologically recent times it has been dammed by a horst beside the Shompole volcano. This has caused the waters to spread out into the steadily expanding Engare Ng'iro swamp, where the river deposits its sediment. The sediment-free river water then seeps into the brine lake. The permanent swamp covers about . South of this a seasonal floodplain of about stretches down to Lake Natron and along its eastern shore.

Possible changes

The Lake Natron basin has been designated a Wetlands of International Importance under the

Ramsar Convention The Ramsar Convention on Wetlands of International Importance Especially as Waterfowl Habitat is an international treaty for the conservation and sustainable use of Ramsar sites (wetlands). It is also known as the Convention on Wetlands. It i ...

. However, in the past there have been plans to dam the Ewaso Ng'iro for hydroelectric power generation and for irrigation of the marshlands north of the lake, diverting water from other rivers to increase the flow. The plans would also include creating a variable freshwater lagoon with an area of about . If implemented, the impact on the lake's ecology could be drastic. Reduced salinity and pollution with agri-chemicals could wipe out the blue-green algae that provide food for the

. The lake is the main breeding ground for this near-threatened species. As of 2007 the dam project appeared to be on hold.

References

{{Authority control Rivers of Kenya