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As an invasive water lettuce spreads along the Vaal River, Rand Water has begun spraying herbicide on the plants and releasing weevils as ‘biological control agents’. While some consider this a necessary response to the problem, others are worried about the long-term effect this will have on the Vaal Rivier.

There have been numerous articles on the issue of water lettuce and some water hyacinths invading the river and destroying the natural species in the waterways after it exploded in the area in 2023.

The problem is clear, but removing this invasive species is proving to be a lot tougher than expected, hence the drastic steps now being taken by Randwater.

Water lettuce forms dense mats that clog waterways making boating, fishing, and other water activities, impossible. These mats also degrade water quality by blocking the air-water interface and greatly reducing oxygen levels, which can result in fish die-off and the overall reduction of aquatic fauna and flora diversity.

Rand Water was given ‘general authorisation’ by the Department of Water and Sanitation (DWS) to manage the water lettuce. This included physical removal, biocontrol and chemical application – led by experts at the Department of Forestry, Fisheries and Environment (DFFE).

The use of Glyphosate-containing herbicide (Round Up) used to combat the plague has however come under fire, with concerns about how the chemical, which is the most used herbicide in the world, could affect drinking water sourced from the river.

Residents along the river, including people who benefit from the tourism the water supports, are now saying the ‘fix’ is creating a bigger problem.

“People are only looking at a section of the puzzle by not looking at the entire [problem] to understand the enormous impact,” said resident Thomas De Toit. “The thing is we’re in crisis mode, and if it was left for decisions, and the volume doubled every two weeks. Time was absolutely against the community.”

“We normally accommodate between 45 to 50 fishermen daily, they come and visit our facility. That number has literally dropped to four or five. So the financial impact of this has been massive.”

Dr Julie Coetzee, a biological control scientist working on the programme says that it’s the most efficient way of combatting the invaders. “The fastest way to knock these plants down is with a herbicide.”

Hoy explained that the whole growth system of the plant is impacted “and in that slowing down, you are giving other mechanisms a chance to come into play such as the biocontrol, and where possible physical removal.

“We just felt that this was really extreme and that we wanted to get it under a more manageable mass.”

One of those opposing the spraying of glyphosate is Bettina Genthe, an independent consultant who previously worked at CSIR, and has 40 years of experience in environmental health related to water quality.

Genthe told Daily Maverick that recent studies have shown that the herbicide could contaminate drinking water sources and air, could cause neurological diseases, and has been categorised by the World Health Organisation as a ‘probable human carcinogen’.

The dose is everything, and if Rand Water was using glyphosate only as an interim measure, and not routinely spraying the chemical, the exposure length would be less harmful. If the dose was repeatedly sprayed, it resulted in a higher dose in total, because there would be adverse health effects in higher doses and on a prolonged basis.

Rand Water is required to use a specific formulation and non-lethal dosage rates, and has stated that the large water body of the Vaal River would dilute this low dose and that the spray was directed at the plants, which had been grouped in targeted areas by the local community, rather than the water body itself.

“Rand Water has not done anything that goes against the law… We really want to do the best thing that we can.”

Dr Samuel Motitsoe, an aquatic ecologist based at Wits University, said “There is growing evidence that the chemical does affect aquatic microbes in the water column and on the sediments which are crucial on important ecosystem structure, functions and processes on aquatic systems. Thus the application of glyphosate in aquatic systems should not be taken lightly, more so that its fate is still under question.”

Last week the first ‘biological control agents’ (weevils) were released outside Stonehaven on Vaal, but scientists are not 100% sure what the glyphosate will do to the weevils as it’s never been tested.

While all of this is only treating the symptoms, the underlying cause of the invasive problem is that the Vaal River’s water is ‘eutrophicated’, which means it contains excessive amounts of nutrients from sewage, agricultural runoff, and industrial waste that flow into the river, which creates an ideal environment for invasives to spread.

Dr Adams believes that “Without addressing the sewage pollution flowing into the Vaal River, the cycle of water lettuce growth in the Vaal River could persist for decades.”

“Hartbeespoort serves as a grim example of what happens when such pollution goes unchecked, leading to severe compromise in water quality. We cannot afford to let other dams and rivers suffer the same fate.”

Hopefully, the cure doesn’t kill the patient.

[source:dailymaverick]