OFF THE SHORES OF LAKE VICTORIA, Kenya — The common water hyacinth, a floating weed that's spreading across the world's largest tropical lake like a moss-green carpet, is known to botanists as "Eichhornia crassipes." Fishermen call it something else.

"That thing is satanic," said Jim Otieno, an angular 33-year-old, to murmured assent from a handful of men gathered by the water's edge in the town of Mbita. They blame the feathery, fast-growing hyacinth for trapping their boats, choking off the fish supply and breeding malaria and other diseases along the southern rim of Lake Victoria.

— introduced by an unwitting farmer and multiplying within months to cover 260 square miles of the lake's surface —

Experts blame a mix of sediment in the water and climatic changes, in the form of unusually heavy rains that helped the plant to proliferate.

After several years and tens of millions of dollars of investment, the hyacinth was finally beaten back by swarms of locally bred weevils