Your sewage is contributing to Hartbeespoort Dam's alien hyacinth invasion

Water hyacinths on Hartbeespoort Dam on 31 January 2023. [Picture: Abigail Javier/Eyewitness News]
Water hyacinths on Hartbeespoort Dam on 31 January 2023. [Picture: Abigail Javier/Eyewitness News]

By Tamika Gounden & Deshnee Subramany


Hartbeespoort Dam, locally called Harties, is a popular getaway destination known for its scenic views and water activities.

For decades, the dam has been infested with an alien plant species that regenerates quicker than it can be removed – the hyacinth.

The flowering plant is beautiful, so much so that the purple blooms were brought here from the Amazon basin for ornamental purposes in aquariums. But soon it found its way into the precious water resource.

“People started throwing it out or flushing it out and everything that comes from upstream, goes through the storm water drains and ends up here in Harties,” said freshwater expert Tsepo Lepono.


The dam was constructed in the early 1920s to provide irrigation to surrounding farms. It has since also been used for recreational purposes, providing landlocked Gauteng and North West residents with much-needed water activities.

“As you can see now, the boats get stuck, and the quality of water makes it difficult to actually use it for irrigation. We can’t use it for these purposes anymore,” Lepono said.

The dam also acted as a conduit for many of Gauteng’s main river systems such as the Hennops, Semylspruit, Kaalspruit, Crocodile and Jukskei rivers. But in recent times, these rivers have been tarnished by sewage leaks streaming into the dam from cities and areas that have faulty piping.

The sewage acts as fertiliser for the hyacinths.

MORA Ecological Services is a consultancy that travels the country weekly to test for water quality assurance. Its executive director, Mogkatla Molepo, told Eyewitness News that if water treatment plans were implemented properly, it would be harder for the hyacinth to grow so rapidly.


The nitrate and phosphate nutrients that are present in wastewater flows into the dam where it feeds the hyacinths.

The plants' regenerative nature means it can never really be completely removed from the dam. One plant can release about 1,000 seeds that will sit on the river bed until they germinate again.

Professor Julie Coetzee, deputy director at the Centre of Biological Control (CBC) at Rhodes University, has for almost a decade doubled up as the leading researcher to investigate the hyacinth plant in the dam. She said various interventions had been tried and tested.

In the late 1980s, bio-control agents were used to tackle the water hyacinth instead of herbicides and chemical trials, killing the plant.

A new agent was introduced after 2018 called Megamelus scutellaris, also known as the water hyacinth planthopper. It is a beetle with a promising future.

“We sent them to Harties every two weeks or so, sending about 6,000 to 10,000 insects in 2019. By the end of 2019 and beginning of 2020, the plants were almost completely obliterated. Most people thought that they had been chemically sprayed; the damage was so great.

We knew that the dying plants was a result of biological control reaching less than 5% cover that year,” Coetzee explained.

But recent heavy rains and floods brought more wastewater into the dam from upstream again, giving the dying species the fuel it needed to regenerate again.

“Unfortunately South Africa has got very polluted water, and this is largely as a result of water treatment works that aren’t compliant with water quality guidelines,” said Coetzee.

What used to be crisp, blue water flowing between the North West mountain tops is now a layer of green bush polluted with litter and dead aquatic animals.

Business owners in the area said the dam used to be one of the biggest tourist attractions in South Africa. It invited international guests to jet ski, enjoy a luxury boat ride, or one-of-a-kind nature walks around the dam.

But now a mat of hyacinths blocks sunlight from getting into the water, which corrupts vital, natural cycles from happening, like photosynthesis. It ultimately kills life underneath it – making the body of water stagnant and stink, which has pushed visitors out of the area.


The financial impact the hyacinth has had on the surrounding community has been burdensome. Boats that used to do three trips daily around the dam are now docked for weeks at a time.

The hyacinth has also been spotted taking over other water beds in Gauteng - and some residents are taking matters into their own hands.

Green Superintendent at Benoni Golf Club Wesley Wipes, who works around Benoni Lake, said they tried to combat the hyacinth growth on the lake.

“We were basically doing it manually when it was on a smaller scale. We tried to remove it manually by sending guys in there with rakes and removing it. And it’s obviously very labour-intensive, very costly and all the rest. But once it got to a point like this, there was nothing else we could do.”

The Department of Water and Sanitation said it had laid out plans for the next few weeks to try to reduce the hyacinth in the dams. These include six task teams deployed to the dam to monitor and clear the plant out. The department has also asked for help to remove the invasive species.

People in cities can also help.

“Watch what you put into your toilets. Watch what you flush down your sinks, and also lobby for cleaner water, lobby for your municipality to fix sewage leaks,” said Coetzee.


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