Bukoba — ACTIVITIES on Lake Victoria are under threat following renewed invasion by the water hyacinth.

Water hyacinth, the weed which once choked Africa 's greatest lake waters, threatening the lives of other organisms and cutting fish production is back again.

Fishermen in Kagera Region have complained that the weed had blocked fish landing beaches and harboured mosquitoes and snakes. The areas worst affected by thick carpets of the weed include Goziba, Bumbire, Nyaburo and Musira, on the Lake Victoria Archipelago.

In 1997 the water weed covered about 2,000 hectares of the lake before it was reduced by 80 per cent nine years later, through spirited control measures. Since then, the weed has been spreading due to continuous inflow of water hyacinth through Kagera River and availability of nutrients which favour proliferation of the weed in the lake.

Studies suggest that water hyacinth was introduced in Africa in 1879, only to find its way to the continent's largest lake 110 years latter. The plant spread started first along the shorelines, forming thick mats that covered an estimated area of 20,000 hectares (about 77 square miles) of the lake by 1998.

By 1995, around 90 per cent of the Ugandan coastline was covered by the plant. It covered substantial areas of the shore, particularly in Uganda , blocking waterways, disrupting hydropower and decreasing the profitability of fishing. Hyacinth also provided refuge for some fish species from the introduced Nile Perch. It largely disappeared from the Lake in the late 90s, perhaps, but not clearly, due to the introduction of a weevil used for biological control.

But in December 2006, according to different satellite images taken, the water hyacinth had returned. The die-off of native plants affects fish and other aquatic animals, according to studies. Water hyacinth clogs irrigation canals and pipes used to draw water from the lake for cities and villages on its shoreline.

Besides, the plants impede water flow, creating abundant habitat for disease-carrying insects like mosquitoes. The weed can also sap oxygen from the water until it creates a "dead zone" where plants and animals can no longer survive. Hyacinth is a free-floating aquatic plant native to tropical South America. It can grow to a height of three feet and has thick heavily branched fibrous roots.

It moves seasonally with the waves from bay to bay, blocking waterways and affecting aquatic life as it sucks oxygen from water.