Water hyacinth (Eichhornia crassipes), a member of the pickerelweed family (Pontederiaceae), is native to tropical America. It has an attractive purple flower which has made it a favourite amongst those interested in ornamental ponds and botanical gardens. As a result humans have spread it widely and coupled with its fast growth rate it now flourishes in all continents but Europe (Lindsey and Hirt, 1999) where it does exist but doesn't flourish as a result of climatic conditions.

Water hyacinth has been in Africa, namely the River Nile, since the 1870's but was not reported in Lake Victoria until 1989 although it is believed to have been present since at least the early 80's (Twongo and Balirwa, 1995). The problems associated with water hyacinth however did not become apparent in Lake Victoria until the early 90's. By 1995 90% of the Ugandan coastline was covered by the plant.

Lake Victoria is at the centre of a large number of communities that live around it. Boarded by Kenya, Tanzania and Uganda it is the second largest lake in the world with a surface area of almost 96,000 km². Lake Victoria is a source of food, drinking and irrigation water, transportation and energy. It is also a convenient disposal site for human, agricultural and industrial waste. Water hyacinth with its characteristic thick floating mats has impacted these uses by; reducing the supply of clean potable water and causing difficulties in water extraction, blocking irrigation canals and increasing transportation costs, reducing fish catches and decreasing available landing sites (Lindsey and Hirt, 1999). It has also increased disputes between local communities, caused an increase in vector borne diseases, reduced tourism and overall been responsible for the translocation of communities away from Lake Victoria. Furthermore local communities have reported a decrease in biodiversity and the closure of the hydroelectric plant at Jinga, due to weed build up, has lead to disruption within the capital of Kampala (Twongo and Balirwa, 1995)

Three basic techniques exist for its control; mechanical, biological and chemical. Chemical control is least favoured owing to the potential damage that herbicides could cause the lake and surrounding agriculture. Mechanical removal has been attempted but is largely ineffective. This is as a result of the cost of mechanical control, due to expensive machinery and manpower and the fact that water hyacinth grows so quickly, doubling in biomass every 6 to 18 days, the exact time being dependent on location and time of year (Lindsey and Hirt, 1999). Biological control is therefore the most favoured method of control. In 1995 the Kenya Agricultural Research Institute (KARI) released Neochetina eichhorniae (mottled water hyacinth weevil) a native tropical American bug that feeds exclusively on water hyacinth. A mass rearing programme was also begun which has now released at least 142,000 weevils at 30 sites along the Lake Victoria shoreline (LVEMP, 2000).

It is believed that water hyacinth has a critical threshold of 5.0 weevils per plant (Mailu, 1999) and recent weevil populations of 5.4 and 6.1 individuals per plant have been reported at Police Pier and Homa Bay respectively (LVEMP, 2000). Indeed water hyacinth has now been considerably reduced and succession of the plant bed mats by Hippograss (Vossia cuspidator) and aquatic ferns and sedges such as Cyperus papyrus and Ipomea aquatica have overtaken water hyacinth in many coastal regions of Lake Victoria. The question still remains however as to why water hyacinth disappeared so quickly. The Ninio events of 1998 and '99 may have played a part or a change in nutrient or ideal growth conditions may have occurred. The weevils may have done their job and reached critical levels. No one knows for sure. As a result no one knows if water hyacinth will return or what conditions are required for the resurgence of water hyacinth. Indeed it appears that very few measurements were taken concerning the growth or decline of water hyacinth and environmental variables associated with these growth patterns.

It is therefore imperative to understand the growth of water hyacinth; what encourages its development and what causes its death. It was under this premise that the post-doc was undertaken. For the most up to date results and data please look at my published papers found on my CV page.