Killer Weed Strikes Lake Victoria
Water hyacinth is taking over world's second-largest lake. Will weevils stop it?
KISUMU, KENYA — When the first British explorers reached the shores of Lake Victoria, they stood in awe before the colossal expanse of clear, cool water lodged in the middle of East Africa.
The lake's extraordinary bounty had already lured nomadic tribes into their first, cautious experiments with sedentary life. It was here that the vast Luo tribe put an end to centuries of continental migration, here that myriad fishing communities came to life all around the lake, and commerce boomed.
Today, damaged by pollution, the majestic body of water is facing an invasion. A foreign weed with an ability to reproduce at extraordinary speeds is baffling authorities, devastating fishing communities, and brutally tampering with the lake's ecosystem.
As the water hyacinth expands - choking up ports, sucking up the water's oxygen, and screening out vital sunlight - an apocalyptic vision is taking form in the minds of a few experts: Lake Victoria, the world's second-largest freshwater body, gradually turning into a gigantic puddle of dead, stagnant water.
"It's a remote possibility, but I can see it happening. The lake would shrivel up ... and turn into a great festering mud puddle," says Gerald Ochiel, a senior research professor at the Kenya Agricultural Research Institute. KARI received $77 million from the World Bank last fall to fight the weed.
A lush, dazzling plant whose brilliant sheen and deep blue flowers made it a favorite in home decoration, the water hyacinth is a native of South America.
No one knows how it made it across the Atlantic into Lake Victoria, but experts suspect it was brought either to Mombasa, Kenya, or neighboring Uganda to decorate homes and hotels.
For six years after its first sighting in the lake, the plant didn't strike anyone as a problem.
By 1995, though, it had become a serious bother: It snarled fishermen's nets and prevented boats from setting out at night.
Miles and miles of plants
Today the weed covers an unknown but significant portion of the lake shared by Kenya, Uganda, and Tanzania. A rough estimate provided by KARI a year ago had the weed covering about 1 percent of the 26,500-square-mile surface.
But because the hyacinth is believed to double in size every 15 days, experts feared that by the end of last year, up to 2 or even 3 percent of the lake could be swallowed up. This translates into a dense wandering mass of more than 769 square miles expanding exponentially across the lake.
Compounding the problem is the fact that Lake Victoria is a shallow body of water, no deeper than 165 feet at any point, with a shoreline of 8 to 16 feet. This means that when it floats to shore, the weed is often unable to move freely, clogging the water.
In 1989, the Lake Victoria Research Team found that in shallower areas where the water level was above 30 meters (98 feet), plants and animals were perishing in oxygen-deprived water.
While the long-term effects of the weed are still hard to gauge, the immediate impact on the fishing communities and the fishing industry is all too visible.
In Dunga Beach, a weed-swallowed nook near Kisumu, fishermen are quickly losing their only means of sustenance.
In the pale morning light, only a few have returned from their nocturnal foray into weed-infested water.
"We went down from 200 kilos [440 pounds] of fish monthly to 120 kilos [264 pounds]," says Nelson Ogwang, secretary of Dunga Beach's fishermen's cooperative.
"Many fishermen have already migrated to areas where the weed has not arrived yet," he says. "Others are still trying to make a living, but their nets get caught in the weed and sometimes their boats are swallowed up."
A month ago, a fisherman who set out at night spent three days stranded in water hyacinths trying to disentangle himself.
The fishing industry on Kenya's 6 percent of the lake has paid for the hyacinth's invasive presence. Losses for the past two years have been estimated at 15 percent, with revenue dropping from $1 million in 1996 to $850,000 in 1997.
"Our fish catch has dropped by over 16,000 tons over 1996," says Edward Wafula, the director of the Kenya Fisheries branch in Kisumu.
"We estimate a $500,000 loss over the next three years unless something is done about this. And it's devastating people's lives," he adds.
Projections such as Mr. Wafula's are conservative at best. They rest on the assumption that the weed will multiply at the present speed, but its exact reproduction rate remains anyone's guess. "We think it can double in volume once every five to 15 days," says Wafula. "But really we are not sure."
The government has been notoriously sluggish in its reaction. "If we had done something from the start, maybe we would not be at this point now," says Wafula. "We all turned away and hoped it would just disappear."
After two years of erratic monitoring, Kenyan authorities turned to Uganda, which has a 43 percent share of the lake and a much more pro-active approach to the problem.
Uganda is encouraging both manual and mechanical harvesting of the weed, ferrying large clumps to shore and putting it to commercial use. The weed can be used both as a fertilizing agent and as a source of energy. Ugandans are also experimenting with chemicals hoping to find a solution that would kill the plant without damaging other organisms.
The natural remedy
With the jury still out on Uganda's dabbling with chemicals, Kenyans are opting for a more environmentally friendly solution, one that features weevils.
The insects are widely considered to be the hyacinth's natural enemy and have been used to combat the plant in Florida.
The weevil hatches eggs in the hyacinth - and only the hyacinth - effectively suffocating it. Once the weed dies, the weevil does too.
"The beauty of all forms of biological control is sustainability," says Samuel Njoka, the head of Kisumu's KARI branch."When things are left to nature, they work splendidly."
Nature's rhythms, however, may be too slow. Experts agree it will take five years for the weevils to reproduce in sufficient numbers to threaten the hyacinth.
By that time, according to the Fisheries department, the Kenyan portion of Lake Victoria could be entirely choked up.
"It's a long time to wait, but there is no alternative," says Mr. Njoka.