Sesmylspruit’s bright-green water ‘potentially harmful’

The bright-green water and orange discharge spotted recently at the Sesmylspruit in Centurion seems to have been cause by sewage or other pollution – but there is some doubt about whether the levels found are high enough to affect health.

Discolouration was noticed by Tarryn Johnston, founder of Hennops Revival, and she alerted various stakeholders, including Dana Wannenburg, MMC for environmental affairs in Tshwane, then who visited the site, close to the outflow of the Rietvlei Dam.

Wannenburg initially said he found nothing wrong with it and called it a natural phenomenon.

He said what was found in the water was not hazardous for humans or animals.

Hennops Revival concerned about what looks like Blue-green algae found flowing down the Sesmylspruit river, from Rietvlei Dam and in to the Hennops River. Blue-green algae is a bacteria found in contaminated water often a sign of serious pollutants upstream, 6 April 2021, Centurion. Picture: Jacques Nelles

However, water samples taken on Wednesday last week by Steven Lea, a water expert, microbiologist and biochemist from an international water and waste management company, found the bright-green water, indeed, had something in it.

Lea said the samples he took indicate pollutants.

“Potentially harmful cyanobacteria were blooming, which produce toxins and consume oxygen, which will kill fish,” Lea said.

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He added the orange slime was a biofilm of filamentous iron bacteria, which may have arisen from iron leaching from the soil or industrial waste Phillip Nel, MMC for utilities and regional operations, said the green floating algae had been observed at this monitoring point for a number of years.

“The Sesmylspruit is monitored twice a month downstream of the Rietvlei Dam,” Nel said.

The proliferation of algae is due to exposure to sunlight and the presence of nutrients, such as phosphates and nitrates, which “indicate the presence of sewage effluents”.

Hennops Revival concerned about what looks like Blue-green algae found flowing down the Sesmylspruit river, from Rietvlei Dam and in to the Hennops River. Blue-green algae is a bacteria found in contaminated water often a sign of serious pollutants upstream, 6 April 2021, Centurion. Picture: Jacques Nelles

Nel added the Rietvlei Dam and the Sesmylspruit received sewage effluent from the Hartebeesfontein Waste Water Treatment Works in Ekurhuleni.

“Data generated from samples collected from the Sesmylspruit show the nitrate and phosphate levels are, on average, within the resource water quality objectives acceptable limits,” Nel said.

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He supplied readings from Rietvlei downstream results from 2020 to 2021 that indicated the pH balance of the water averaged from 7.81 to the most recent reading laast month of 8.66.

A study of Critical Analysis of Environmental Water Quality in South Africa by the Water Research Commission (WRC) indicates a pH of less than seven is acidic, while a pH greater than seven is alkaline.

According to WRC the pH of most raw water sources lies within the range of 6.5 to 8.5 and the pH of water does not have direct health consequences, except at extremes.

By Marizka Coetzer