Fish deaths at Hartbeespoort Dam linked to sewage contamination

Investigations by the department of water & sanitation have found that the deaths of fish at Hartbeespoort Dam on April 11 were due to extremely low oxygen levels in water.

The department released the investigation report on Tuesday, after reports that thousands of fish had died.

The department’s spokesperson, Wisane Mavasa, said samples were taken at the dam edge near the overgrown hyacinth, 60m from the edge of the dam, at the Ifafi Aquatic Club jetty, as well as where the fish deaths occurred near the Ifafi Aquatic Club. 

Mavasa said the test results revealed that excessive algal growth caused by high nutrient (phosphorus and nitrogen contents) levels in the water led to oxygen depletion and fish mortality. 

“This occurrence of low concentration of oxygen in water is typical in sewage-contaminated systems with high organic matter, and could not be attributed to high water temperatures given the average temperature of 22ºC at the time of sampling,” said Mavasa.

She said to address the hyacinth and algal growth at the dam, the department recently appointed Magalies Water for three years to develop and implement a programme that will deal with the invasive plant and the algae that is infesting the dam. 

“The entity is expected to develop a resource management and remediation plan to address the poor water quality, minimise and control the plant and algal growth in the dam and the upstream catchment which lead to its pollution and compromise water quality and use of the dam,” she said.

The programme is expected to start by mid-May and will incorporate the biological control programme managed by the department of forestry, fisheries & the environment.

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