A study jointly funded by the Department of Science and Technology and the Council for Scientific and Industrial Research (CSIR) has found that harmful cyanobacteria, or blue-green algae, which are toxic to humans, are widespread in South Africa’s 50 largest dams.

The study, through the use of innovative remote sensing techniques, found that, for instance, the Hartbeespoort dam, in the North West, Darlington dam, in the Eastern Cape, and Spitskop dam, in the Northern Cape, are severely affected by cyanobacterial surface scum, with intermediate to extensive coverage.

University of Cape Town earth observation scientist Dr Mark Matthews, who conducted the study as part of his PhD study, which was funded by the CSIR under the supervision of CSIR principal scientist Dr Stewart Bernard, found that South Africa’s water quality is a significant concern.

“Serious steps need to be taken to reduce the amount of nutrients entering our lakes. Water that is rich in cyanobacteria poses a serious health risk and can result in death if consumed in large quantities,” warns Matthews.

Matthews’ study, titled ‘Eutrophication and cyanobacterial blooms in South African inland waters: 10 years of MERIS observations’, observed remotely sensed earth observation data to monitor chlorophylla, cyanobacteria and surface scum in the 50 largest standing water bodies in South Africa between 2002 and 2012.

The study relied on data from time series observations of parameters related to phytoplankton and water clarity derived from the medium resolution imaging spectrometer full resolution (MERIS FR) satellite instrument. It also found that eutrophication and cyanobacterial blooms are widespread and extensive in South African water bodies, and poisonings of domestic and wild animals are a frequent occurrence.

Eutrophication is nutrient enrichment that may lead to an increase in harmful algae in an aquatic system. These nutrients enter water bodies from agricultural and wastewater sources.

Cyanobacteria is a group of blue-green algae that occur in highly visible blooms mainly in aquatic ecosystems that can be toxic to fish and other species and pose serious human health risks.

Further, the study confirmed that Hartbeespoort dam is a hypertrophic system dominated by frequent and persistent cyanobacterial blooms and surface scum conditions.

Meanwhile, the highest chlorophyll values were associated with the Mthatha and Ncora dams, in the Eastern Cape, the Erfenis, Allemans-kraal and Krugersdrift dams, in the Free State, and the Ntshingwayo dam, in KwaZulu-Natal.

A total of 18 water bodies had between 10% and 30% average cyanobacteria area coverage. These water bodies had common and regular cyanobacterial blooms with medium coverage and include South Africa’s two largest reservoirs; the Gariep and the Vaal dams

The study, however, excluded seasonal pans, estuaries, and water bodies subject to tidal influence.

Matthews advises that the relevant managing authorities need to take immediate measures to reduce the risk of exposure to surface scums.

“Focus should be placed on reducing exposure to surface scums at Hartbeespoort, Darlington and Spitskop. “This can be done by improving the treatment of water at sewage plants, identifying the point of entry of nutrients into the water bodies and mitigating this,” advises Matthews.