World's Most Abundant Lake Threatened by Weeds

Environment News Service

By Brian Ligomeka

BLANTYRE, Malawi, November 8, 2000 (ENS) - Noxious water weeds are choking the life out of Lake Malawi, home to the largest number of fish species of any lake in the world. But a program set up four years ago to tackle the spread of water hyacinths on the lake, which is Africa's third largest, is showing signs of success.

The weeds threaten the aquatic life of Lake Malawi and the Shire River, a tributary of the Zambezi River. The water hyacinth (Eichhornia crassipes) could make both water bodies unnavigable.

According to the UK-based World Conservation Monitoring Centre, Lake Malawi probably contains more than 500 fish species from 10 families with perhaps half occurring in Lake Malawi National Park, a designated world heritage site at the southern end of the lake.

It is home to the world's largest population of cichlids, a large family of freshwater, perchlike fishes that number up to 1,500 species. Non-cichlid species include catfishes, minnows, mormyrids, true eels and spiny eels. The park protects many hundreds of these fish species, nearly all of them unique to Malawi.
According to the United Nations Educational, Scientific and Cultural Organization, which designated the park a world heritage site in 1984, Lake Malawi's importance in the study of evolution is comparable to that of the finches of the Galapagos Islands.

Malawi's Minister for Natural Resources and Environmental Affairs, Harry Thomson, calls the weed a curse.

"Let’s consider the presence of water hyacinths in the waters of Lake Malawi as a curse to the nation and the international community, especially when we consider the devastating impact of the weed on aquatic life," said Thomson.

Water hyacinths cover large parts of the lake, blocking sunlight and hindering the growth of plankton, an important part of the food chain. They also affect hydroelectric and irrigation projects.

"When growing rapidly, it absorbs large amounts of nitrogen and phosphorus," said Roger Day, a senior official of Agricultural and Biological International, Africa Regional Centre. "The reduced oxygen content can have a major detrimental effect on the biodiversity of an aquatic ecosystem.

"The presence of water hyacinth can reduce water flow which causes suspended particles to be precipitated, and increases siltation. The sheer volume of water displaced by the weed can reduce the effective capacity of reservoirs, causing water levels to fall more rapidly in dry weather," said Day.

Thomson said the water hyacinth has caused the decline of fish populations in Lake Malawi and is even affecting tourism.

"People from all corners of the world in the past used to flock to Malawi to swim, bathe and enjoy themselves at our beautiful lake, but there is a danger now that if the hyacinth completely invades Lake Malawi, even tourists would not find Malawi to be a nice touristic destination," said Thomson.

Fishermen who ply their trade in Lake Malawi and the Shire River complain bitterly that the weed disturbs their smooth sailing.

"The massive presence of the water hyacinth has totally marred our business," said Buleki Jestino, a fisherman from Mangochi in southern Malawi. "It is extremely difficult to travel parts of the lake, which are highly infested by the weeds."

To combat the weeds, the government set up the Malawi Water Hyacinth Control Programme in 1996. The program's operations manager, Patrick Maseko Phiri, said much progress has been achieved.

"We have plunged all our efforts in combating the weeds," said Phiri. "We began our battle by spraying chemicals on the water hyacinths in some parts of the country. We abandoned the method after it had proved to be ineffective and also expensive in the pilot project."

The program resorted to physical and biological control of the water hyacinth. Communities along Lake Malawi's shores and the river banks of the Shire helped to uproot and burn the water hyacinths.

"We sensitized the local communities on the dangers of the water hyacinths and encouraged them to join hands with the government in eliminating them," said Phiri. "They cooperated with us and formed village beach committees, which besides uprooting the weed controls other fishermen from overfishing."

The program has also adopted biological control techniques. Phiri ordered water hyacinth beetles from South Africa and bred them locally before releasing about 200,000 into the most infested areas.

"Biological control is the most permanent way of destroying water hyacinths," said Phiri. "The beetles destroy the weeds by feeding on the leaves while the larvae of the beetles destroy both stems and petals of the weed."

The only disadvantage, said Phiri, is that the beetles take a long time to completely destroy the weeds.

Despite its reputation as a noxious pest, the water hyacinth is valued elsewhere for its potential benefits, which include energy production from biomass, fertilizers and livestock fodder.

Biomass is a renewable energy resource derived from numerous sources, including the byproducts from the timber industry, agricultural crops, raw material from the forest, major parts of household waste and wood.

Blantyre city assembly director of leisure, culture and environment Robert Kawiya said that in Sudan, water hyacinth from the Nile River is being used in biomass energy production for cooking, lighting and refrigeration.

Water hyacinth waste has been used as organic fertilizer on farms, he said, while dried hyacinth can be used for growing mushrooms. In China, the water hyacinth is a prized raw material for livestock fodder.

Kawiya said poverty stricken Malawians could learn from other countries who have realized the water hyacinth's potential.

Although Malawian law forbids people from growing water hyacinths, many collect the weed and plant it to brighten up their homes.

© Environment News Service (ENS) 2000

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