Yala Swamp

Category: Inland Aquatic Biomes.

Geographic Location: Africa.

Summary: The Yala Swamp is one of Kenya’s largest wetland areas, rich in flora and fauna, but it is threatened by large-scale development for commercial agriculture.

The Yala Swamp is a large wetland located in western Kenya; it lies to the northeast of Lake Victoria. The Yala Swamp forms part of the wetlands that contribute to the catchment for Lake Victoria, which is the second-largest freshwater lake in the world. Lake Victoria is an essential source of sustenance, both in terms of water and food, for tens of millions of people and uncounted wildlife in the Lake Victoria basin and beyond. The Yala Swamp itself is surrounded by a human population whose density exceeds 175 individuals per 0.4 square mile (1 square kilometer), one of the highest densities in eastern Africa.

The Yala Swamp is the third-largest wetland ecosystem in Kenya, and is a rich and diverse habitat for a wide range of flora and fauna. These include globally threatened species, as well as many that are typical of the Lake Victoria biome. The Yala Swamp has been isolated from Lake Victoria for some time, however; it is connected to a small lake, Lake Kanyaboli, that buffers and isolates it from the main body of Lake Victoria.

Several species that are extinct in the larger lake ecosystem are still found in the Yala Swamp, and some thrive in the adjacent Lake Kanyaboli, including various species of cichlid fishes. Among these are dozens of species that were negatively impacted by the 1950s introduction of the Nile perch into Lake Victoria.

The Yala Swamp biome consists of a complex of intact marshes and small lakes, and some disturbed areas in two zones of western Kenya: Siaya District in Nyanza Province and Busia District in Western Province. The Yala Swamp covers 19,768 acres (8,000 hectares) and lies 3,707–3,806 feet (1,130–1,160 meters) above sea level. Lake Kanyaboli covers about 2,471 acres (1,000 hectares), and is about 10 feet (three meters) deep. Studies have found the level of oxygenation in the waters of the Yala Swamp wetlands varies from highly oxygenated in its main channels and in Lake Kanyaboli, to very low in some of the stagnant areas of the swamp.

Biodiversity

The vegetation in the swamp is dominated by tall, dense, mono-dominant stands of papyrus (Cyperus papyrus). In some shallower areas, stands of tall reeds (Phragmites spp.) are common, along with a mixture of aquatic sedges and grasses. This dense vegetation, in particular the extensive network of papyrus, serves as a natural filter that holds silt and other sediments and pollutants back from surrounding habitats, releasing clean water to flow on into Lake Victoria.

Dragonflies and damselflies are abundant in the swamp. These insects have aquatic nymphs and are good indicators of water quality. One of the most common species along the edges of the swamp is the banded groundling (Brachythemis leucosticta), a dragonfly that can be found in such large numbers that swarms of them rise from the ground when an animal walks through the grass.

The Yala Swamp has been declared one of Kenya’s Important Bird Areas; it is a site of both high diversity and high bird numbers. The avian life of the swamp includes notable species like the papyrus gonolek, papyrus yellow warbler, papyrus canary, great egret, and Bailon’s crake, as well as numerous other ducks and migratory wetland birds such as the great snipe. The sitatunga, an antelope adapted to a semiaquatic lifestyle, is an emblematic mammal found within the swamp.

Fish species in Lake Kanyaboli include a tilapia (Oreochromis esculentus), part of the thriving local fishing industry. Many fish species breed in Lake Kanyaboli and the adjacent channels of the Yala Swamp. As the Nile perch is still absent from the swamp itself, the Yala Swamp’s wetlands are a vital location for conservation of the fish species that are threatened, or likely even extinct, in Lake Victoria.

Human Activity

The Yala Swamp and its adjacent areas contain large amounts of nutrient-rich sediments, deposited by the Yala River over time. This has made the swamp a location for the development of commercial agriculture. The cash crops that are grown under intensive production include rice, cotton, and sugarcane. All of these crops are cultivated using irrigation with water drawn directly from the swamp or river channels. The Yala Swamp currently is the focus of large-scale agricultural development partnerships between the Kenyan government and multinational corporations. Some parts of the swamp have already been drained and are being cultivated. The changes to the swamp have negatively impacted local communities, greatly increasing the amount of flooding in some places. At the same time, human development and climate change have also reduced local fish populations.

Global warming is expected to increase average temperatures in Kenya by several degrees over the course of the twenty-first century, continuing the trend that is as much as double the global average rate of increase. Precipitation has declined in recent years. It is thought that drier conditions and drought may prevail. These trends are likely to affect the Yala Swamp biome by a combination of increasing evaporation rates, declining river flow levels, and destruction of wetland capacity to regenerate. All these factors will need to be taken into consideration if the area is to be sustainably developed and its vital habitats conserved.

Bibliography

Abila, R., et al. “The Role of the Yala Swamp Lakes in the Conservation of Lake Victoria Region Haplochromine Cichlids: Evidence from Genetic and Trophic Ecology Studies.” Lakes & Reservoirs: Research and Management 13 (2004).

Aloo, P. A. “Biological Diversity of the Yala Swamp Lakes, with Special Emphasis on Fish Species Composition, in Relation to Changes in the Lake Victoria Basin (Kenya): Threats and Conservation Measures.” Biodiversity and Conservation 12 (2003).

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

Cheng, Kang-Chun. “These Kenyan Villagers Are Used to Flooding. This Is Different.” Christian Science Monitor, 31 Aug. 2021, www.csmonitor.com/World/Africa/2021/0831/These-Kenyan-villagers-are-used-to-flooding.-This-is-different. Accessed 18 Aug. 2022.

Shorrocks, B. The Biology of African Savannahs. Oxford, UK: Oxford University Press, 2007.