Weevil released to combat Hartbeespoort Dam hyacinth invasion

Weevils to rid Hartbeespoort Dam of invasive water hyacinth

In a renewed effort to tackle the persistent water hyacinth infestation at Hartbeespoort Dam, the South African Department of Water and Sanitation, in collaboration with Rhodes University’s Centre for Biological Control (CBC), has introduced weevils into the water.

According to a statement, Water and Sanitation Deputy Minister, Sello Seitlholo, today, 17 March 2025, joined Professor Julie Coetzee, Deputy Director of the CBC, at the Hartbeespoort Dam to officially release the Salvinia weevil insect into the dam.

The weevil species, a subaquatic herbivorous insect that feeds on the invasive aquatic plant, is also regarded as an effective classical biological control agent used in several countries.

“The invasive alien plant said to be from South America was first recorded at Hartbeespoort Dam in 2011, and has since spread through areas of the North West and Gauteng provinces, and has reached the Limpopo River, which marks the border with our neighbour Botswana, threatening South Africa’s water bodies.” the Water and Sanitation department said in their statement.

“CBS is one of many research laboratories that dedicated several years to testing a biological control agent Cyrtobagous salviniae (Florida biotype) and was granted approval for release of the insect late in 2024.” the statement said.

What exactly is water hyacinth?

As mentioned, common water hyacinth is an aquatic plant native to South America, that has naturalised throughout the world and is often invasive outside its native range.

The main reason for its rapid growth at Hartbeespoort has been an influx of nutrients into the dam. Sources include untreated sewage from surrounding settlements, agricultural runoff, and fertiliser from golf courses and gardens. These nutrients also create ideal conditions for the hyacinth to flourish.