• About 50% of South Africa’s biggest dams could be dangerous to those who swim in them.
  • South African dams have high levels of cyanobacteria, a type of algae that feeds of nutrients such as fertiliser and sewage run-off. 
  • A real-time map, created using satellite data, aims to show which dams could be dangerous - but the site will go dark by the end of the month as government funding runs out.

A real-time map of nutrient pollution in more than 100 dams in South Africa shows that two in five could pose high health risks from toxic algae, and about half are not safe to swim in. 

Cyanolakes, a South African company that specialises in determining water quality and algal bloom from satellite data, created the map. It was developed as part of the Earth Observation National Eutrophication Monitoring Programme, funded by the Water Research Commission. But the government funding has run out, and at the end of this month be information will no longer be free.

A map of SA dams. (Cyanolakes)

A 2014 study found that 50% of South Africa’s water bodies had pervasive toxic algae, which thrived due to eutrophication. Eutrophication is an excess of nutrients in the water, often caused by fertilizer and sewage run off, among other factors. This bacteria can be toxic to humans and animals.

Some of the SA dams that pose health risks. (Cyanolakes)

Mark Matthews, founder of Cyanolakes, produced the 2014 study as part of his doctorate. He developed a method to determine the quantity of algae in water bodies from satellite data, and used it as the basis for Cyanolakes. This technique “allows [water utilities and companies] to monitor their water more effectively than traditional methods”, he says.

“[The map] is really about providing real time online service which gives you info about cyanobacterial blooms in the interest in protecting public health,” he says. “There is tons of satellite data, but it is sitting there doing nothing. We wanted to use that and serve it up so that the public can make decisions.”

The department of water and sanitation said it was considering options for the project. "We are however restricted by available budgets and no decision has yet been made," said Gerhard Cilliers, scientific manager for resource quality monitoring at the department.

Asked if the South African situation had gotten worse since his PhD, Matthews says that it is about as bad as it was then. “The thing is, it is quite difficult to make generalisations.”

But he notes that the current levels are those for Spring. “[The quantity of algae] will be higher in summer. When the most people are in the water, it will be the worst.”

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