Last week on Friday (9 October), I did an aerial survey of the degraded rivers that continuously pollute the Hartbeespoort Dam, causing the explosive growth of water hyacinth and salvinia.
A local pilot offered to fly me, and we departed from Grand Central Airport, surveying the interconnected waterways including the Kaalspruit, Jukskei, Hennops and Crocodile rivers.
I saw unnatural foaming at various points, long stretches of murky water, and widespread illegal dumping.
At Alexandra, I was alarmed by the huge mountain of illegal construction rubble that looks perilously close to collapsing into the Jukskei river. If this happens, it could block the river and flood parts of Alexandra.
A major source of pollution affecting Hartbeespoort Dam is the roughly 90 million litres of untreated sewage that flows into it every day from three malfunctioning wastewater treatment works in Johannesburg. Overflowing pump stations, agricultural fertiliser runoff, and industrial pollutants add to the burden. High levels of nitrogen and phosphorus cause hyper-eutrophication which fuels the explosive growth of water hyacinth and salvinia. Fish die because oxygen in the water is depleted.
I was shocked by the vast green blankets of water hyacinth and salvinia covering parts of the dam. It would be even worse without Magalies Water’s innovative efforts to biologically control these invasive plants, including the deployment of millions of microscopic water hyacinth planthoppers. But controlling the plants treats the symptom, not the cause, which is the devastating pollution from the inflowing rivers.
A systematic effort is needed to ensure that municipalities repair and properly operate their failing wastewater treatment works. The 2025 Green Drop Report found that 23 of Gauteng’s 61 wastewater systems are in a critical state. Hotspots that need special attention include the Zandspruit pump station in northern Johannesburg. There also needs to be a crackdown on the major industrial polluters.
The priority must be to stop pollution at source, enforce compliance, and restore the health of the rivers that feed Hartbeespoort Dam. No amount of clearing invasive plants will solve the problem while sewage and industrial pollution continue to flow into the dam.
