South Africa has released thousands of weevil insects to restore the ecological balance of the Hartbeespoort Dam.

The South African Water and Sanitation Department says the Salvinia weevil insects were deployed to consume Salvinia minima, an invasive alien aquatic weed threatening South Africa's freshwater ecosystems in the Hartebeespoort Dam water system.

Deputy Minister Sello Seitlholo and experts from the Centre for Biological Control oversaw the release of the Cyrtobagous salviniae weevil, a biological control agent known for its effectiveness in managing invasive plant species.

“You will recall that in the Hartbees Dam in early January there was plenty of fish that actually died. That is because of the inability of the water resource to produce oxygen,” explained Deputy Minister Seitlholo.

“Because what these alien invasive species do is that they do suck out the oxygen. This has obviously led to us as the Department of Water and Sanitation, having to come up with remedial processes that involve biological control,” Seitlholo added.

The weevils are subaquatic herbivorous insects that specifically target and feed on Salvinia minima.

Authorities say the invasive weed, native to South America, was first detected in Hartbeespoort Dam in 2011 and has since spread rapidly across the North West and Gauteng provinces, reaching the Limpopo River, which borders Botswana.

The Centre for Biological Control says it will closely monitor the weevils' progress and assess their impact on the Salvinia minima population.