Chris McGreal
A triumph of nature over technology has left a multimillion-rand World Bank scheme to combat giant weeds clogging Lake Victoria trailing behind an army of small bugs.
The release of weevils into Africa’s largest lake has dramatically reversed the all-consuming spread of the water hyacinth, dubbed the “Aids of the water” in Uganda and Kenya because it destroyed fishing, cut off island communities and wrecked local economies.
But despite the success of the insects, the World Bank is continuing to fund giant mechanical harvesters to shred the remaining weeds against the advice of some experts and local fishermen.
Scientists and environmentalists say the dredgers are not only a waste of R50- million of World Bank money because the weevils have already done away with more than half of the weed, but the machines carry their own dangers. One group, Environmental Economics for Eastern and Southern Africa, said the harvesters dump tons of weed on the lake bed which could damage marine life and alter the ecosystem.
The hyacinths are believed to have been brought to Rwanda by Belgian colonists as ornamental plants and then worked their way into the lake by river. They have blossomed over the past decade, fed by the flow of sewage and pollutants into Lake Victoria, and fertiliser and soil washed into the water.
Just a few months ago, the water hyacinth, also known as Eichornia crassipes, seemed unstoppable. Sprawling islands of rippling green plants – some as large as 25ha – drifted across Lake Victoria until they lodged themselves against the shore, cutting off entire villages from their fishing grounds. The hyacinth also carried snails harbouring the deadly disease bilharzia.
Local economies suffered because farmers could not get their crops to market by canoe. Uganda’s hydro-electric dam was regularly clogged and repeatedly had to be shut down for the turbines to be cleaned. The weeds were blamed for power cuts.
A single hyacinth multiplied to up to a million plants each year. The carpet of weeds was so dense that from some Ugandan lakeside villages barely half the water between the shore and horizon was visible.
The mats of hyacinth brought traffic at the Kenyan lake port of Kisumu to a standstill, leaving railway wagons destined for Tanzania stranded. Many of the port workers lost their jobs.
Then came the weevils reared by the Kenya Agricultural Research Institute. There was considerable scepticism when the first 100 were let loose on the hyacinths three years ago. Since then 100 000 have been released on to the weeds, and they have multiplied into several million.
The bugs have proven more successful than expected by stunting the hyacinth’s growth and eventually killing it. Weevils also stop the plant reproducing.
“The reduction has been significant,” said Tom Moorhouse, head of the Uganda office of Aquatics International, an American firm monitoring the hyacinths as part of a United States aid project. “The weevils grazed on the leaf and laid eggs on the stem and the pupae bored into the stem. But there also seems to be a cumulative effect. Other insects have got into the hyacinths. The El Nio rains raised the level of the lake almost 2m. That’s a lot of water that could have diluted the nutrients the plants feed on. Before the lake was at a 40-year low and then it went almost to an all-time high.”
Weevils have been released in South Africa to successfully counteract hyacinths since the late 1970s. Dr Martin Hill from the Plant Protection Research Institute has been working with the Department of Water Affairs and Forestry in breeding the weevils for release in problem areas in KwaZulu-Natal, on the Vaal river, in Mpumalanga and, most recently, in the Eastern Cape near Stutterheim.
When Uganda and Kenya were desperate to find a solution to the hyacinth problem several years ago they explored two other options. Uganda tried herbicides, with limited results and persistent fears about pollution.
Both countries also put their faith in mechanical harvesters designed to cut and shred the hyacinth. But the weevils have left five of the machines virtually redundant. They were of limited use, in any case.
Two Dutch harvesters cleared about 30ha of the weed from around the hydroelectric plant at Uganda’s Owens Falls. But within a few months the hyacinth had completely reclaimed the area.
Four years ago, Britain despatched a harvester stamped with the Prince of Wales Award for Innovation. It was designed to scoop up pond weed and algae from rivers, but ground to a halt on its first outing into the rather more resistant hyacinth. The contraption was left to rust among the weeds. An American machine broke down because of “high water flows”.
The World Bank paid for the latest two harvesters as part of its 500-million World Bank project to clean up Lake Victoria, revive its fisheries programmes and protect its biodiversity. The machines were introduced at Kisumu even though the weevils had already made their mark.
The World Bank despatched an Australian expert, Michael Julien, to assess the impact of the weevils last year. He concluded that the bugs had made the mechanical harvesters near obsolete.
“I’ve personally visited various sites in the lake and witnessed heavy damage on the plants. There is very little water hyacinth now as compared to the beginning of last year. This is why mechanical harvesters are lying disused all over. It is all wasted capacity.”
But Tom Moorhouse says while the machinery has taken second place to the weevils, it still has its uses. “The harvester at Port Bell hasn’t been used much this year. It’s the same at Owens Falls, although the excavator is still necessary. But an integrated solution means biological control with mechanical and some chemical control.
“The machinery is capable of reducing hyacinth and it should continue to be considered,” he said.
The harvesters might also still be useful to contain the papyrus and hippo-grass which is springing up in place of the hyacinth.
The water hyacinth was not all bad news. Imaginative uses were found for the plant. Ugandan prisons discovered that when the weed was mixed with cow dung it produced enough gas to cook for all its inmates.
And now the Kenyan fishermen whose livelihoods were nearly wrecked by the hyacinth are pleading to prevent its final destruction. They say the weed provided the perfect habitat for a type of catfish which had almost disappeared, and for which there is now a lucrative market.