Botswana’s north-western tourism attraction, the Okavango Delta, has suffered a temporary setback as it is presently infested with a free floating water weed called Salvinia molesta, whose presence poses a threat to the lives of the delta’s fish and disturbs its attractions, like canoeing and boat cruising.
The Salvinia molesta is a floating, rootless aquatic fern, whose plant populations can “overgrow” and replace native vegetation, resulting in surface cover that prevents light and atmospheric oxygen from entering the water. Decomposing material drops to the bottom, consuming dissolved oxygen needed by fish and other aquatic organism.
However, a Maun based researcher in the Department of Water Affairs, Dr Chandra Jayne Naidu, dismissed the presence of the weed, also known as the Kariba weed, as a temporary setback that will be contained in the near future.
“Three pilot cites have totally gotten rid of the weed in Linyanti, Chobe and Kwando rivers. We are using biological and physical means to remove the weed. We are breeding weevils (insects) in pools at Takanaka in the Moremi Game Reserve and we will carefully release them into the infested waters,” said Dr Naidu.
He added that the eradication project is being funded by many agencies coordinated by the United Nations Development Programme (UNDP). Dr Naidu added that they cannot use chemicals to get rid of the Kariba weed because they affect other useful plant species and fish. The government stopped the use of chemicals in the 1990s due to their effects on the environment.
Dr Naidu explained that the greatest effect of chemicals is that they reduce oxygen to less than 1mg/litre and increases carbon dioxide levels.
The Kariba weed was first discovered in 1949. It cannot be totally eradicated, but it can be easily controlled.
While the rivers that are affected supply water to the north-western parts of the country, the Department of Water Affairs remains confident that the weed will not compromise the quality of water supplied to these regions.
Covering 17,000 square kilometres (6,564 square miles), the Okavango is the world’s largest inland delta, and is home to an array of wild animals, among them the red lechwe antelope, wild dogs, elephant and sitatunga, or marshbuck.
The Okavango Delta originates in Angola’s western highlands, where water flows from the Cubango River into neighbouring Namibia’s Kavango River before entering Botswana.