Fighting water weeds in West Africa

Water weeds are an environmental nightmare. They make waterways unnavigable, reduce the generating capacity of hydro-electric stations and block irrigation canals. By clogging sewage and drainage systems, they can cause flooding, contaminate drinking water and create breeding grounds for harmful insects and bacteria.

Water weeds also contribute to water shortages. Aquatic weeds absorb water and then release it through a process called transpiration. As a result, water losses can be more than three times higher in weed infested water bodies.


In West Africa, river systems cross many national borders, so international cooperation is essential in the fight against water weed infestations.



Water Hyacinth infestation at boat landing site, Tano lagoon, Ghana

FAO/22203/R. Labrada



Water hyacinth with leaves damaged by water hyacinth weevils

FAO/22205/R. Labrada



For more photos, go to slide show: Water Hyacinth in Developing Countries


"Preventing the spread of water weeds has become a development priority all over the world," says Dr Ricardo Labrada, Weed Officer with FAO's Plant Protection Service. In West Africa, the Plant Protection Service is providing technical support for a water weed management project in the inland waters of Burkina Faso, Ghana and Togo. The two-year project, which began in July 2000, is funded by FAO through its Technical Cooperation Programme.

In West Africa, fishermen have been particularly hard hit by water weed infestations. The weeds slow down their boats and make landings difficult, and as a result, more of their catch goes bad. Fishermen also need to use more fuel, up to three times as much, to push their boats through the heavy weeds. Their increased costs are then reflected in consumer prices.

The weeds that cause the most problems are water lettuce, a native to Africa, and the water fern and water hyacinth, which come from South America. Experts suspect the water hyacinth, perhaps the most environmentally damaging water weed, was brought to West Africa in the 1980's by botanists and gardeners as an ornamental plant. "It's a case where a beautiful flower has managed to do tremendous harm", says Dr Labrada.

Insects versus water weeds

Project planners aim to use biological control to fight aquatic weeds. This involves releasing insects that feed on these aquatic weeds into the affected bodies of water. During an earlier FAO water weed management project in Ghana, which ran from 1994 to 1997, the insects released were successful in controlling both the water fern and water lettuce. The water hyacinth however, presents a tougher challenge. It can take between five and six years to control this extremely invasive weed using biological methods.

"It's important to have realistic expectations about what can be achieved," says Dr Labrada,. "Once water hyacinth has become established, it is almost impossible to eradicate it completely. Our objective is to use biological methods to contain the spread of water hyacinth and other aquatic weeds and minimize the damage they cause."

An international challenge

Water weeds don't recognize national borders, so international cooperation is essential to bring them under control. In the past, Ghana's fight against water weeds, particularly the hyacinth, has been hampered by the fact that aquatic weeds often enter the country through rivers flowing from Burkina Faso and Togo. The Black Volta and the White Volta both have been infested by water hyacinth.

Neither Burkina Faso nor Togo has established programmes for controlling aquatic weeds.The project aims to help them establish national committees on water weed control and strengthen Ghana's existing committee. Breeding centres for insects, such as the water hyacinth weevil and the salvinia weevil, that like to eat these weeds will also be set up in all three countries.

Specialists who have worked on FAO water weed management projects in the region will be hired through the Organization's Technical Cooperation among Developing Countries partnership programme to train technical staff from each country in biological control methods.

Community support is essential

"Success at the regional level can only be achieved if we have participation at the local level," says Dr Labrada. Consequently, the project will carry out an awareness raising campaign in rural areas on the threats water weeds pose to public health and local livelihoods. One of the campaign's aims is to encourage local communities to help monitor the presence of weeds in their area and to enlist local fishermen to help release insects into affected areas.


Lake Victoria: success in the battle against water hyacinth

In the late 1980s water hyacinth invaded Lake Victoria, one of the world's largest bodies of freshwater. Floating in large, dense mats, the weeds interfered with fishing and transportation, clogged the intake at the Owen Falls Dam power station, and provided a breeding ground for malaria-carrying mosquitoes. Lake Victoria was facing a serious environmental crisis. In 1995, FAO became one of the major technical executing agencies in a five-year project to control water hyacinth in Lake Victoria using biological methods. This project has succeeded in reducing water hyacinth in the lake by more than 60 percent.


Boat landing site heavily infested by water hyacinth, Lake Victoria, Uganda

FAO/22204/R. Labrada



16 August, 2000

Related links

 FAO Home page 

 Search our site 

Comments?: [email protected]

©FAO, 2000