Lake Turkana

Category: Inland Aquatic Biomes.

Geographic Location: Africa.

Summary: The world’s largest desert lake is a source of life and sustenance in a remote and harsh landscape, and is now threatened by climate change and large-scale development of its tributaries.

Lake Turkana is one of Africa’s most remote and enigmatic lakes. It is located within a hot, dry desert landscape in the Great Rift Valley in the northwestern part of Kenya, just south of the border with Sudan and Ethiopia. The lake sits in an area of volcanic activity that has shaped its existence over time and contributed to the unique ecology and chemistry of the lake.

Lake Turkana has a surface area of 2,606 square miles (6,750 square kilometers) and a volume of 49 cubic miles (204 cubic kilometers). The maximum depth of Lake Turkana is 358 feet (109 meters), and there is a mean depth of 98 feet (30 meters). The lake level fluctuates, with changes of 3–5 feet (1–1.5 meters) commonly observed. The catchment area for Lake Turkana is large and located a great distance from the lake in the western highlands of Kenya and the southern highlands of Ethiopia, covering an area estimated to be more than 50,193 square miles (130,000 square kilometers).

The main tributary of Lake Turkana is the Omo River, which enters from the north, originating in the Ethiopian highlands. The Omo contributes more than 90 percent of the total water flowing into the lake at present. There are many other streams and seasonal rivers originating from mountains and hills around the lake, but all of these are temporary, or seasonal, flows.

The second-largest river flowing into Lake Turkana is the Turkwel River, which originates from the Cherangani Hills in Kenya. The Turkwel River has been dammed at the Turkwel Gorge about 93 miles (150 kilometers) west of the lake. This dam was intended for hydroelectric power generation, but it still has not filled to the levels that were expected.

Notably, Lake Turkana has no outlet—it is an endorheic, or closed basin—and this means that water is lost from the lake mainly by evaporation. The evaporation rate has been estimated at 92 inches (2,335 millimeters) per year. Water levels of Lake Turkana are, therefore, determined by the balance between the inflow from rivers and groundwater and evaporation from the lake’s surface. Evaporation rates are high and compounded by the fact that the lake is exposed to high strong winds from the southeast. These factors all contribute to the fact that the level of Lake Turkana is extremely sensitive to climatic variations, droughts, and human-made interference with the rivers and catchment area.

Lake Turkana is located in one of the planet’s hottest and most arid areas. The mean annual rainfall in the region directly surrounding the lake is less than 10 inches (250 millimeters), and years can go by here with no rains. Rainfall is typically unpredictable and can be locally heavy and torrential when it does fall.

Weather data from the town of Lodwar in northern Kenya shows a seasonal pattern, with the lowest temperatures experienced in July and August, and a wide range from 68 to 104 degrees F (20 to 40 C), with a mean daily temperature of 84 degrees F (29 degrees C). In some areas, the daytime temperature can exceed 122 degrees F (50 degrees C), and soil surface temperatures of up to 158 degrees F (70 degrees C) have been recorded.

Despite these harsh conditions, Lake Turkana is a thriving ecosystem and an important global site for the study of evolution. The Lake Turkana region is most famous for fossil discoveries that have provided insights into the origin and evolution of hominids, including our own species, Homo sapiens sapiens. Hominids have been present around the lake for several million years, and the fossil record of the area, brought to light by the work of the Leakey family, is extraordinary.

Biodiversity

The current flora and fauna of the Lake Turkana region includes a wide range of species that are both unique to the lake as well as typical of the dryland biome of northern Kenya and the Somali-Maasai center of endemism, which means hosting species found nowhere else on Earth.

Lake Turkana supports a large, thriving local fishery. The two most important commercial species are the Nile perch and Nile tilapia, both of which occur naturally in the lake. The annual fish catch was estimated at 16,535 tons (15,000 metric tons) in 1988, but records are scarce, and it is unclear what the current fish catch trends are today. More than 40 species of fish have been recorded from the lake and its tributaries, including several endemic species.

The vegetation of the lake includes a community of phytoplankton that provides the basis and primary production for the food web in the lake. Lake Turkana is fringed in areas by vegetation with a submerged plant called Potomageton. These areas are important spawning ground for fish and occur in more sheltered bays. The deltas of the Omo, Turkwel, and Kerio rivers have swampy, vegetation-including areas of papyrus and bulrushes. However, today the deltas are rapidly being overtaken by invasive species, including the thorny shrub Prosopis and the water hyacinth. The invasive species are having a serious effect on the ecology of the deltas and the local fisheries.

Insect life includes large numbers of dragonflies and damselflies. Some of the species that occur in the lake are more closely related to those in the Mediterranean rather than those of tropical Africa, which further indicates the uniqueness of the biogeography of this desert lake.

Bird life at Lake Turkana is abundant, and it is one of the region’s Important Bird Areas. Large numbers of the pink-backed pelican, greater flamingo, spur-winged plover, and little stint occur on the lake. More than 30 paleartic migrant species from Europe and Asia make use of the lake on their journey south through Africa. Several important waterbirds breed on the lake and its islands, including the African skimmer and goliath heron.

Lake Turkana contains three islands: North, Central, and South Islands, which are all national parks. The islands are an important nesting area and sanctuary for Nile crocodiles, of which the lake was estimated to contain 14,000 in 1968. The islands are remote and difficult to protect, and invasion by goats or disturbance by fishers is a major issue for the species on these islands.

Human Settlement

The communities surrounding the lake are increasingly shifting from a nomadic, pastoralist, and artisanal fishing lifestyle to a sedentary lifestyle. There is limited cultivation of millet, sorghum, and other crops in the deltas and areas near the rivers. This area has also been recently a zone of drought and famine, possibly exacerbated by climate change, and remains one of the least-developed parts of East Africa.

A 2021 report from the United Nations Environment Programme found that global climate change may result in increased flooding, which had been a relatively rare occurrence at Lake Turkana. The region was impacted by flooding in both 2019 and 2020. The UN report said that an increase in heavy rains could result in more water inflow to the lake, raising the likelihood of more severe flooding over the next two decades.

Bibliography

Beentje, H. Kenya Trees, Shrubs and Lianas. Nairobi: National Museums of Kenya, 1994.

Bennun, L. and P. Njoroge. Important Bird Areas in Kenya. Nairobi, Kenya: East Africa Natural History Society, 1999.

“Climate Change Could Spark Floods in World’s Largest Desert Lake: New Study.” United Nations Environment Programme, 19 July 2021, www.unep.org/news-and-stories/story/climate-change-could-spark-floods-worlds-largest-desert-lake-new-study. Accessed 29 Aug. 2022.

Hopson, A. J., ed. Lake Turkana; A Report on the Finding of the Lake Turkana Project 1972–1975, Vols. 1–6. London: Overseas Development Administration, 1982.