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Water hyacinth, known scientifically as Eichhornia Crassipes, is among the worlds most noxious invasive weeds. Native to the tropics of South America, it now thrives on every continent except Europe. It was introduced on Africa around 1879, and 110 years later, established itself on the continent’s largest lake, Lake Victoria. Spreading along the shorelines, the plant formed thick mats that covered an estimated 20,000 hectares of the lake by 1998.
Aggressive removal efforts, the release of the Neachitina weevil, which eats plants and environmental factors, cut the plant back to manageable levels. Winam Gulf the northeast corner of Lake Victoria in Kenya was the most severely affected region during the first hyacinth outbreak in 1998, with as much as 17,231 hectares of the plant growing on its surface. By 2000, the area covered by water hyacinth was down to about 500 hectares and in December 2005, the lake appeared to be clear.
But in December 2006, the water hyacinth was back, this may be attributed to the unusually heavy rains of November and December 2006 that flooded the rivers that feed into the Gulf. The rains and floods raised the water levels on the lake and swept agricultural run-off and nutrient-rich sediment into the water. As a result, vegetation around the lake was dramatically greener due to the rains. The influx of fertilizer and sediments not only turned water brown, but it also fed a fresh outbreak of water hyacinth.
The plant poses lots of problem to the lake. The mat vegetation is so thick that fishermen cannot launch their boats or bring fish to the market on shore. Sunlight does not filter through the plants, so native plants in the lake don’t get the light they need. The die-off of native plants affects fish and other aquatic animals.
Water hyacinth clogs irrigation canals and pipes used to draw water from the lake for cities and villages on its shore. The plants impede water flow, creating abundant habitat for disease-carrying insects like mosquitoes.
Water hyacinth can also sap oxygen from the water until it creates a “dead zone” where plants and animals can no longer survive. Typically only aggressive measures can control the fast-growing plant.
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