Review of the impact of water hyacinth on Lake Victoria: the case of Winam Gulf, Kenya.

Abstract

Water hyacinth, Eichhornia crassipes, invaded Lake Victoria in 1989 and has had significant social, economic and environmental impacts, which remain largely unquantified. The biological control administered by Kenya Agricultural Research Institute (KARI) coupled with other control measures have reduced water hyacinth levels from 6000 ha to a current estimate of 400 ha., on the Kenyan Side of the lake. The objective of this study was to document the impact of water hyacinth. Data was derived from personal interviews with key respondents, Annual Reports and other publications from the relevant departments in the Ministries. The analysis involved comparing data between two periods, without water hyacinth (1986- 91) and the period with water hyacinth (1992-99). The results indicated that there was an increase of total fish production from 140597 to 168019 tons signalling an increase of 20% over the two periods. However, significant increases were reported in Nile Perch and Prototerus, while significant decreases were realized with Mormyrus and other mixed fish species. The results also showed that there was an increase in the incoming cargo and a decline in the outgoing marine cargo handled at the Kisumu pier as shown by the available data covering the period 1996-1998. Water supply to Kisumu municipality decreased by 25% in the year 1999, although time series data was not available. The increases or decreases in fish production and water supply points to the fact that water hyacinth may have had an effect. On the contrary, there were mixed and unclear trends on the incidence of water hyacinth related diseases (malaria, bilharzia, cholera and gastro-intenstinal disorders) which could not be directly associated with water hyacinth when the two periods are compared. This was due to inadequate data resulting from recent subdivision in the various districts and the fact that it was not easy to apportion the disease incidence resulting from water hyacinth and other related causes. The study suggested the need to obtain reliable time series data on water hyacinth infestation and initiate specialized studies to establish the impact of water hyacinth on bio-diversity, water quality and supply, ecological succession and health and nutrition (343).