Highly polluted reservoirs in Gauteng and the North West, including Hartbeespoort Dam, should be fenced off because of the health risks they pose to people and animals from blooms of toxic cyanobacteria. Photo: Getty Images
Highly polluted reservoirs in Gauteng and the North West, including Hartbeespoort Dam, should be fenced off because of the health risks they pose to people and animals from blooms of toxic cyanobacteria (blue-green algae).
This is according to Bill Harding, a limnologist with a special and long-term interest in eutrophication and cyanobacteria.
“A dam like Hartbeespoort, Roodeplaat and Rietvlei, to an extent, and the Klipvoor Dam [near Brits], any of those 18 in that set there, should all be closed. There should be no recreation on them at all,” he said.
In any other country, that understands the problem, Hartbeespoort Dam “would not be fenced off, but fenced off with signage and any recreation on the dam would be prohibited because the risk to human health is just too great. But we’re not seeing that here.”
Harding added that the time he saw signs routinely warning the public about the potential health risks of Hartbeespoort Dam was in 2001.
That’s the crux of the problem. “This is not a problem that is only in the new South Africa; this comes from the old South Africa as well — the same problem has been coming since 1958, roughly.
“There’s been no admission that the problem actually exists, so until the water and sanitation department can man up to this and say, ‘Okay, we’ve got this wrong for a really long time’ and stop with these projects like they’ve got at Hartbeespoort Dam, which is just cosmetic, just trying to sweep the plant [water hyacinth] out so the dam looks nice but there’s no actual effort to deal with the cause. It’s … Panado for cancer; it’s never going to work.”
He said the department had admitted in the National Water Resource Strategy that eutrophication — nutrient enrichment or too much food from wastewater in the dams — is its main water-quality problem.
The department “realises if they come and say, ‘Oh hang on, we’ve got this problem in Hartbeespoort Dam,’ then they’ve got to admit the problem occurs in all the others. Then they’ve got to admit to the cause, which is the fact that they haven’t regulated the wastewater treatment plants anywhere in the country, pretty much ever … They cannot protect against eutrophication.”
It’s a cross-cutting problem that requires an admission from “the president to all the parliamentary committees”, he said.
“It’s not just water. It’s health, it’s agriculture, it’s recreation, it’s tourism — it’s all those things that are affected. Plus, water from a dam like Hartbeespoort is going into an international river. That water is going to Mozambique; you’re seeing this problem down there … in terms of international law, you shouldn’t be doing that.”
Cyanobacteria, invasive aquatic weeds
“There’s so little informed understanding of what’s happening in that reservoir [Hartbeespoort] and it’s not only that reservoir. It’s one of dozens that look the same.”
Cyanobacteria and invasive water hyacinth “can co-exist perfectly happily”. One is a plant and one’s a bacteria — one lives in the water and one lives on the water.
“If you remove the water hyacinth, you can induce a [cyanobacteria] bloom mainly because you’re removing the light shading. The bacteria like to have light … and they will start growing.”
When he first worked at Hartbeespoort Dam in 1975, it was knee-deep in water hyacinth and had “one of the biggest blooms you’ve ever seen that was underneath that.
“It was what was discovered for the first time in South Africa — it’s called a hyperscum. We could actually stand our equipment on the scum — it was like an ice sheet — and you could stand things next to the boat on the scum.
“They are both growing because there’s way too much food in the dam. There’s all the wastewater coming down from the catchment, which is all inadequately treated human waste, and there’s just too much fertiliser, and both plant types [have] got so much food they don’t know what to do with it.”
Harmful blooms
Cyanobacteria in various forms exist in all water bodies, even unpolluted ones. “They’re just in very low numbers because they’re limited by the nutrient availability, so you don’t see it.
“It’s countrywide. We’ve got them down here in Cape Town’s two biggest dams. Theewaterskloof and Voëlvlei Dam are both problematic because they both produce [blooms], but not big blooms, nothing like Hartbeespoort or Roodeplaat, or any of the 18-odd dams up in Gauteng or the North West that are grossly polluted.
“But they still produce enough growth to be problematic with either the taste and odour of the water, which is most common, or the risk of toxins in the water,” Harding said, explaining that it costs authorities an enormous amount of money to treat the water continuously.
“The summer-rainfall ones tend to be a lot worse than the winter-rainfall ones down here [in Cape Town]. But go to KwaZulu-Natal — all those dams are all loaded with blue-greens because they are full of wastewater.”
Hazards of cyanobacteria
Problematical bloom forms — those that form scums — or harmful algal blooms can produce a range of toxins. “The most common ones are known as microcystins. Those are the ones that affect the liver — they cause necrosis. They are the ones we’ve known about the longest.
“There are other types that produce nerve toxins; there are alkaloid toxins — the list is endless. We still haven’t found all of them.”
The blue-green algal cells are endotoxic (or the outsides of the cells) and “if you go into a dam, if you’ve got a sensitive condition or maybe not even … you can develop these enormous blisters just from walking through the bloom.
“You’re not coming into contact with the toxins; you’re coming into contact with the cells. I’ve seen guys working in vleis in the Western Cape where they went in and it looks like they’ve been burnt in a fire because their whole body just turns into these blisters.”
Although harmful algal blooms are “extremely noxious”, a lot of the time they don’t do anything and “we don’t get indications of poisonings occurring”, but Harding pointed out that farmers can lose large numbers of stock animals.
There are images from the late 1950s and 1960s of dead cows all around the Vaal Dam. “That’s because there was just enough nutrients coming from that massive catchment … to create enough food in the dam for the bloom to form, and for the toxins to be there, and then the animals drink it.”
Animals have a sort of magnetic attraction to these dangerous blooms and, because of the smell and taste, they drink the water. “Dogs like the smell, so they try to get it on their skin. As they rush in, they get a mouthful of it and then the dog passes away.”
Toxic algal species
Department spokesman Wisane Mavasa said it routinely tests freshwater resources in the country, especially in dams, for the presence of toxic algal species.
Most of the known water bodies prone to eutrophic or hypertrophic conditions are monitored for the broader cyanobacteria genera as part of the National Eutrophication Monitoring Programme, she said. It establishes the trophic status of dams and the presence of toxic cyanobacterial blooms are detected.
“Most of the hypertrophic systems are found in the Crocodile-West Marico catchments of the country.”
Where contact water recreation activities are concerned, the World Health Organisation established three hazard levels against which water users can assess the danger posed by cyanobacteria and the recommended actions that should be taken. “At unacceptable levels of cyanobacteria, the use of water must be prohibited and measures are being taken to warn potential users of the dam or water resource.”
Main drivers
Various sources contribute to the increase in nutrient levels in the country’s water bodies, which can lead to the presence or cases of cyanobacterial blooms.
The main drivers are partially or untreated sewage, agricultural run-off containing fertilisers, detergents rich in phosphate and nutrient-rich industrial effluents. A certain amount of nutrients also comes from natural sources.
“Enriching water bodies with nutrients create an environment that is conducive for growth of aquatic plants, hence there is an infestation of rivers and dams with blue-green algae (cyanobacteria) since they feed with the ingressing nutrients,” Mavasa said.
The problem is “extremely big in South Africa” and prevails in 80% of the country’s dams.
“The department of water and sanitation enacted the Green Drop assessment, which is a tool that identifies key deficiencies and avenues of consideration to improve operations. Initiatives to enhance capacity are also underway with problematic entities.”
Hartbeespoort remediation
The Eutrophication Management Strategy for South Africa, which was finalised and approved by the department in February last year, is being implemented countrywide, Mavasa said.
On Hartbeespoort Dam, the department had appointed Magalies Water to assist with its remediation and the upper catchment of Crocodile West. “The department and Magalies Water have implemented nanobubble technology to improve the water quality for the benefit of all users.
“This technology retards the growth of algae, aquatic plants and its by-products through the attenuation of nutrients … through their sequestration and oxidation due to ingression of acceptable levels of oxygen …
“The algal counts and its toxins, as by-products, have reduced drastically after the implementation of nanobubble [technology] and the biogeochemical processes of the aquatic system are restored and the dam is able to render its native intrinsic values,” Mavasa said.