LAKE OSSA, Cameroon—A Cameroonian lake choked with invasive weeds is a science project for biologists, but for Charles Elingua, it means starvation. “I have been fishing in this lake for more than 30 years,” Elinga, 56, and leader of fishermen in Lake Ossa, said. “The salvinia weed has disrupted fishing considerably.  I once was able to save up to FCFA 10,000 (US $17.99) from fishing daily. But today, it is pretty difficult to even fetch FCFA 1,000 (US $1.80) from the activity, which can hardly afford three square meals for my family,” the father of eight lamented. Since appearing in the lake in 2016, Lake Ossa, one of the largest natural lakes in Cameroon, has been invaded by a fast-spreading waterweed called salvinia molesta. Nearly 70 per cent of the Lake’s 4,000-hectare surface is now engulfed by this floating aquatic fern that thrives in slow-moving, nutrient-rich, warm freshwater. But the …