Earthwatch-supported researchers make recommendations for the sustainable management of Kenya's only freshwater Rift Valley lake

Kenya's Lake Naivasha, a wetland of international importance recognized by the Ramsar Convention and a historically renowned hotspot for tropical biodiversity, has been degraded by decades of environmental impacts. In a recent paper in Ecohydrology & Hydrobiology, Earthwatch-supported scientists review decades of research on the ecology and hydrology of Lake Naivasha and suggest measures for the lake's sustainable management.

"This is the first time a paper has put together the perceived and future problems of the fishing industry on Lake Naivasha with the real problems caused by the introduction of alien species," said Dr. David Harper (University of Leicester), principal investigator of Earthwatch's Lakes of the Rift Valley project. "Our findings clarify what is going wrong with the lake and therefore point the way clearly forward."

Harper and his co-author Dr. Kenneth Mavuti (University of Nairobi) found that the hydrology of the lake has been drastically altered by the degradation of papyrus swamps growing around the perimeter and at the inflow of rivers. This papyrus loss began in the 1980s, at the same time as a lake level decline of up to three meters due to horticultural irrigation and power plant cooling from the lake. Rivers and rainwater runoff now run directly into the lake, without the benefit of papyrus swamps, bringing silt and nutrients that choke the sunlight and alter the food chain.

The paper also highlighted the ecological impact of exotic species, especially the Louisiana crayfish, introduced in the 1960s and responsible for eliminating most of the native aquatic plant species. An introduced fish, the largemouth bass, eliminated the only fish endemic to Lake Naivasha, the small-toothed carp, in the 1960s. Now largemouth bass and other exotic fish, including the common carp, are the basis of commercial fishing operations in the lake.

In their paper, Harper and Mavuti make three clear recommendations for returning the beleaguered lake to sustainability: limiting irrigation for agriculture to achieve sustainable lake levels, restoring papyrus swamps at river inflows, and controlling illegal fishing. The latter is necessary to allow the population of large predatory fish, such as largemouth bass, to grow and control the destructive Louisiana crayfish. These recommendations have been positively received by the local management agency, the Lake Naivasha Riparian Association, and their national and international supporters.

Earthwatch volunteers were instrumental in contributing to all of these findings, particularly the long time series of data on the Louisiana crayfish and data on the papyrus degradation collected in 2002. "Earthwatch teams have been critical in enabling us to amass many data points," said Harper, "for example on long transects where each volunteer had a particular responsibility for recording one factor."

Earthwatch teams also contributed to a recent article in the Journal of the East Africa Natural History Society, on mapping the depth of Lake Bogoria, another of Kenya's Rift Valley lakes. Bogoria is one of only a dozen or so alkaline lakes in East Africa that can sustain populations of threatened lesser flamingos, because of its substantial depth and apparent stability.

Despite Bogoria's reputation for stability, however, Harper's findings from this year confirm local rumors that the lake occasionally "dies," becoming very smelly, and all the flamingos leave. Earthwatch teams in March and April 2004 recorded overcast days when the lake was totally devoid of oxygen, followed in July by a complete collapse of Spirulina, the blue-green bacteria that flamingos feed on.

As of November, the Spirulina was recovering and flamingos were returning to Bogoria. But as with the Lake Naivasha results, these findings underscore the importance of monitoring the ecology of each of Kenya's unique Rift Valley lakes, in order to assure their restoration and future sustainable management.

Earthwatch Institute is an international nonprofit organization that supports scientific field research by offering members of the public unique opportunities to work alongside leading field scientists and researchers. Earthwatch's mission is to engage people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment.

For more information, see
"Lake Naivasha, Kenya: Ecohydrology to guide the management of a tropical protected area."
David Harper and Kenneth Mavuti.
Ecohydrology & Hydrobiology (2004) 4:255-273

learn more about Lakes of the Rift Valley.