ABSTRACT

ABSTRACT Invasive aquatic weeds have spread throughout the world's waterways as a result of anthropogenic activities. The three most problematic species are water hyacinth, floating water fern and water lettuce. With the potential to double in biomass in a matter of days and the ability to migrate easily due to their free-floating vegetative form, they can successfully colonize new habitats, form dense mats along shorelines and displace native vegetation. In doing so, they effect ecological processes within lakes and decrease the biodiversity. Moreover, for human populations living around such lakes, they reduce the access and quality of available drinking and irrigation water, prevent fishermen from making a living, clog water intakes at hydro-electric dams, increase vector-borne diseases and generally lead to an increase in human suffering. Cultural eutrophication of lakes is also a major problem around the world and can amplify the problem of nuisance floating plants. Weed growth can expand rapidly with an

increase in loading of nutrients such as nitrogen and phosphorus. In Africa, there are many examples of eutrophication leading to elevated weed biomass and the subsequent problems that this entails. In Lake Victoria, East Africa, water hyacinth was a major problem in the 1990s that has now largely subsided. However, there are signs that eutrophication, as a result of anthropogenic changes in land use, is still increasing. At a minimum, this will probably continue to maintain the presence of water hyacinth within the lake but it also has the potential to bring about a resurgence to its nuisance status. If this occurs then the human suffering experienced could be above and beyond that seen during the 1990s. Methods to manage water hyacinth include physical, chemical and biological forms of control. However, for the long-term sustainability of Lake Victoria, including the control of water hyacinth, only improved land, air and watershed management can provide the solution to reducing eutrophication and the potential of water hyacinth outbreaks. The measures needed to effect the changes necessary for nutrient control require a massive financial injection. The countries bordering Lake Victoria have a direct responsibility towards it and should contribute in every way to its restoration, as the result of non-action will be regionally devastating. However, there are also implications for the global economy; therefore, solutions also need to involve a wider arena.