Rosemary Anderson navigated her speedboat through the clumps of floating water lettuce clogging the Vaal River.
But Anderson, the managing director of Stonehaven on Vaal, slowed as she reached the Taaibos, a tributary that runs into the Vaal River, where the invasive alien aquatic plant, together with water hyacinth, another aquatic invader, is on “steroids”.
“I’m not sure I want to go further in case I get stuck,” she said, approaching a thick carpet of water lettuce. In recent weeks, in the war they’ve waged on the weed, the Vaal River community has cordoned off the water lettuce at the Taaibos to stop its explosive spread further into the river. “Look at it, it’s like a field,” Anderson said, shaking her head.
Water lettuce, originally from South America, is a floating herb in rosettes of grey-green leaves, which form dense mats, completely covering a water surface. It clogs waterways and irrigation equipment, reduces water flow, impedes navigation, fishing and other recreational activities and provides a breeding place for mosquitos and bilharzia-carrying snails, according to Invasives South Africa.
Anderson, the national chairperson of the Federated Hospitality Association of Southern Africa, said there is a very limited window of opportunity to urgently remove the weed, which is “currently very accessibly contained” in up to five kilometres in the Taaibos and about 30km of river from where the Taaibos enters the Vaal River Barrage Reservoir to the Barrage.
But if allowed to pass the Barrage, the plant has access to a journey of about 1 000km of the middle and lower Vaal river, the Bloemhof Dam and then into the Orange river. “Many towns, communities and farmers abstract from these waterways for both drinking water and irrigation. This will have a negative impact on them including complicating water abstraction with pumps and pipes getting clogged with water lettuce.
“That is why this is a national crisis, because if the water lettuce is not urgently removed from the Vaal River Barrage Reservoir, there is the chance that these water sources below the Barrage will be unnecessarily negatively impacted.”
Four-pronged plan
The authorities, Rand Water and the department of water and sanitation (DWS), did not take the necessary remedial action from February 2021, when the water lettuce was first brought to their attention. But there seems to be some urgency now, with the DWS approving the general authorisation that Rand Water needed on 8 February in a relatively short time.
“Now Rand Water is permitted to implement their multi-pronged simultaneous approach of physical extraction/removal, containment of water lettuce in certain areas, introduction of weevils and spraying of herbicide.”
In the past three weeks, the community had been removing numerous tons of water lettuce, including using heavy earth moving equipment to maximise tonnage removed – all at their own cost.
“Rand Water has now agreed to partner with the local Vaal river community where, together, they will implement the necessary remedial action approved by DWS in the form of the general authorisation under Rand Water’s strict supervision and criteria.”
This includes the spraying of herbicide under strict general authorisation criteria with Rand Water on site to oversee the process and that it is strictly adhered to. The spraying started on Tuesday.
She said this is a first where the Vaal river community, the government and Rand Water have worked together in a “very hands-on way” on solving an invasive aquatic weed.
“The community has no intention of this water source deteriorating as other dams and rivers have done before – that is why they have a significant fund-raising machine and have an ‘all-hands-on-deck’ approach to being part of the aquatic weeds removal.”
Inaction
When water lettuce first appeared, apparently via the Suikerbosrand tributary, during the floods in 2021, Anderson raised the issue in writing with both DWS and Rand Water.
But no action was taken, apart from Rand Water enlisting Rhodes University to help set up a weevil centre at their head office. But this project faltered as staffing issues arose at Rand Water. “A few weevils were released in 2021, but not enough to make a significant difference and the floods did not help matters either.”
As the water lettuce largely dies over winter in the colder Vaal areas, “it appeared to have disappeared”. It resurfaced in the summer of 2022 and significantly in the summer of 2023/4. Seeds are often deposited into river beds, which germinate when the temperature is conducive to growth.
Since at least the 1980s, Rand Water had a team of 12 who monitored the Vaal River Barrage Reservoir by boat daily. “It worked very well. That’s why today we’re not the same as Hartbeespoort Dam because they did preventative maintenance. In 2014, the river was in such a good state from a non-aquatic weeds point of view, that they decided, ‘let’s just remove the team because the river doesn’t need it anymore.’”
Had the team been on the river, “we would not be in this current situation where tens of millions are now going to be spent to address this problem”.
Integrated approach
While Rand Water did not respond to the Mail & Guardian, it confirmed in a Facebook post that the herbicide spray would be done in accordance with the approved general authorisation from the DWS and with technical information from the department of forestry, fisheries and the environment.
It had embarked on an integrated approach to manage the water lettuce infestation, including physical removal, biocontrol and chemical application and experts agreed “that this type of approach is most suitable at present”.
The application of all herbicides has been approved by both departments and they are “set at a sub-lethal dose because we are implementing an integrated approach. The sub-lethal dose actually increases the sugar and carbohydrate contents of the Pontederia crassipes plant making it more palatable for the biocontrol agent.”
‘Polluting disaster’
But WaterCAN, an initiative of the Organisation Undoing Tax Abuse, is alarmed by the use of glyphosate over the Vaal River to combat the water lettuce and water hyacinth problem, citing significant environmental and public health concerns. “Despite assurances that this action is being undertaken in accordance with the approved general authorisation … WaterCAN remains steadfast in its opposition to this approach.”
Spraying glyphosate directly into a freshwater ecosystem is a “terrible idea”, agreed Simone Dahms-Verster, a lecturer at the University of Witwatersrand’s School of Geography, Archaeology and Environmental Studies. “The effects of glyphosate and its metabolites can cause reactive oxygen species and gene mutations in various aquatic species.”
It’s “a short-term solution and a long-term polluting disaster”, said Ferrial Adam, WaterCAN’s executive manager. “Halting sewage pollution from Emfuleni and neighbouring municipalities is paramount in reducing nutrient loading and curbing the growth of water lettuce.”
Integrated pest management strategies, mechanical removal, and biological control options offer environmentally-friendly alternatives that minimise harm to ecosystems and safeguard public health. But using glyphosate is “like amputating a limb when you’ve got a scratch”, Adam said. “They’re really going to kill the ecosystem, which is already struggling because of all the sewage pollution … then there’s industrial waste, other chemicals and now you’re just adding to this whole poisoning.”
Biocontrol to the rescue: tiny weevils
Rand Water said biocontrol agents – water lettuce weevils and plant hoppers to tackle water hyacinth – would be released on Thursday.
Julie Coetzee, the deputy director of the Centre for Biological Control (CBC) at Rhodes University, said the water lettuce weevils are a natural enemy of water lettuce and have been used very successfully as long-term biological control.
The adults chew holes in the leaves, laying their eggs in the leaves. “Then the little larvae hatch and they make tunnels. When there’s enough of them, the plants get very damaged and they’ll get water-logged and sink … Instead of the plant producing flowers and seeds, they put their energy into making little daughter plants, but the size of the plants goes from the size of a cabbage now, to these tiny little plants with tiny little daughter plants on them so they just get smaller and smaller.”
While the extent of water lettuce is “huge” on the Vaal river, “we’re saying just give these insects time to build up,” Coetzee said. “We don’t have inundative numbers now but we can get there and let these control agents do their job because we know how effective it is.
“But the landowners want it gone … They’re much louder and so they’ve pretty much demanded the spraying … but then you’ve got the environmentalists on the other hand saying: ‘What are you doing putting thousands of litres of glyphosate into our drinking water when it’s got such a bad reputation?’”
Chemical spraying is a wicked problem, Coetzee noted, though short-term as the long-term plan is biological control. “If you spray it with a sub-lethal dose, it benefits the biological control agents but there aren’t any bio-control agents on the system. So, you’re essentially wasting thousands of litres, because there’s no biocontrol impact to top off. These plants will be slightly weakened but they’re not going to die.”
Biocontrol reserves are being set aside. “That’s where we are going to release agents and we’re going to make it known to people using the Vaal to leave these areas alone because this is where we’ve released biocontrol agents.”
The hope is they will become little nurseries that the tiny insects can disperse from. “At the same time, we’re setting up mass-rearing stations with Rand Water and with some of the private landowners who want to rear weevils on their property.”
Wisane Mavasa, spokesperson for the DWS, said that it has no record of being alerted to the water lettuce phenomenon in 2021, however “it must be known that invasive vegetation is the responsibility of the DFFE in terms of legislation”.
“Since the issue has an impact on water resources, the department is working with the DFFE through memorandums of agreements to ensure the control of alien invasive species on our rivers and dams to ensure that the risk of impact is removed.”
The presence of alien invasive species in the country’s rivers and dams have been a “problem for a long time”, she said.
“These invasive alien plants are not indigenous to this country, therefore, there are no natural controls that can keep it under control. Most of these plants are floating and have no roots anchored in soil and can therefore move around freely adding to its efficiency to spread.”
The DWS is treating the water lettuce issue in the Vaal River seriously and since the problem became known “there has been a collaborative effort between the DWS, DFFE and Rand Water to address it”.
Rand Water as the land owner of the Vaal Barrage (who are the owners of the land currently infested), together with the DFFE, has a Vaal River management plan in place, which is being implemented.
“The short-term intervention is to remove the water lettuce within the ambit of the general authorisation in terms of the National Water Act by making use of a combination of approved biological, chemical and physical controls.”
High nutrient levels in the Vaal River created an enabling environment for these plants to further thrive because of the nutrients in the river system. The long-term plan is to address the cause of the infestation, which is a result of pollution from municipal wastewater works in the catchment.
“DWS suspects that the biggest cause of water lettuce infestation is eutrophication (high nutrients) because of excessive amounts of nitrogen and phosphorus into water as a result of the release of inadequately treated wastewater from sewage plants.”
The DWS, she said, has implemented the Vaal Intervention Project to address wastewater infrastructure failures in the Emfuleni Local Municipality area under Section 63 of the Water Services Act.
“DWS appointed Rand Water as implementing agent for the national government funded project to assist Emfuleni to address its wastewater challenges through refurbishment and upgrading of wastewater infrastructure such as waste water treatment works, pump stations, sewer pipelines and associated infrastructure to reduce pollution to the environment and the water course.”