First signs of success in fight to save world’s most abundant lake

Lake Malawi is said to contain the highest number of fish species of any lake in the world, with up to 500 species from ten families including cichlids, catfish, minnows, true eels and spiny eels. Half are found in Lake Malawi National Park, which is a designated world heritage site at the southern end of the lake. Nearly all are unique to Malawi. However, the water hyacinth threatens the lake’s rich aquatic life and that of the Shire River, a tributary of the Zambezi. If the infestation continues, both could also become unnavigable.

Water hyacinth is a particularly invasive weed that is covering large parts of the lake, blocking out sunlight and hindering the growth of plankton, which is important to the food chain. When growing rapidly, the weed also absorbs large amounts of nitrogen and phosphorus, which promote the growth of algae on which plankton feed. In addition, it also interferes with hydroelectric and irrigation projects.

This lake’s rich heritage is threatened by the current weed infestation. Roger Day, a senior official of Agricultural and Biological International, Africa Regional Centre, said: “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.”

However, the Malawi Water Hyacinth Control Programme, which was set up in 1996 to combat the weed, is now said to be making significant progress. An initial programme of spraying proved ineffective, so the programme took to direct action – volunteers in communities around the lake’s shores uprooted and burned the water hyacinth.

Communities were also educated about the dangers the weed brought, and encouraged to join in the battle to rid the lake of its unwanted green overcoat. Biological controls were also employed – the programme’s operations manager, Patrick Maseko Phiri, bred water hyacinth beetles, obtained from South Africa, and released 200,000 into the areas with the highest density of weed.

Mr Phiri said: “Biological control is the most permanent way of destroying water hyacinths. 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 is that process of destruction is a long one.

The possibility of encouraging people to use the remaining weed for energy production, fertiliser and a feed for livestock is also being actively considered.