plants overrun Vaalkop Dam

This was to manage and reduce the spread of the water hyacinth.

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While these biocontrol agents — natural enemies of the water hyacinth — were released and although three rearing stations were established, there simply weren’t enough stakeholders around the dam to set up enough to supplement what the centre sent.

“We've been dosing the dam for four years but we just haven't been able to hit the same infestation of insects on Vaalkop as was witnessed on Harties,” Frere said. “Harties had 2 500 bugs per square metre; we’ve only managed to get it up to 700. It’s just from a lack of resources.”

In June last year, the CBC surveyed dams and rivers in the North West and highlighted that a new invader, common salvinia, was spreading down the Crocodile River from Hartbeespoort Dam, as well as down the Hex River from another invaded site, the sewage-polluted Bospoort Dam.

Officials were made aware of the severity of the invasion, which had also reached the Limpopo River that forms the national border with Botswana.

In January, Vaalkop Dam’s water level stood at a very low 25% but by April, following the late summer rains, it was overflowing. This increase in water, rich in nutrients, allowed both water hyacinth and common salvinia to explode. The amount of aquatic weeds on the system soared from about 100 hectares in January to 1 000 hectares at the end of May.

The mat is a mixed carpet of water hyacinth and common salvinia, which blocks out light, preventing oxygen from being produced in the water column. This causes most of the aquatic life in the system to die, turning the dam, which is a birding, fishing and wildlife hotspot, into a “largely lifeless” body of water.