Blue-green algae bloom at Rietvlei

The City of Cape Town has urged visitors at Rietvlei to avoid the algal bloom there. Picture: Frieda Prinsloo

Anyone going into the water at Rietvlei does so at their own risk because of an algal bloom there, says the City.

“Detailed sampling” of the water body was planned for this week to gauge toxicity and spread of the algae, said mayoral committee member for spatial planning and environment, Marian Nieuwoudt. Anyone using the water body would have to sign an indemnity form at the gate, she said. Blue-green algae blooms usually present as green flecks in the water and can form blue-green, white, or brown foam, scum or mats, floating on the surface of the water.

Exposure to these algae, especially when toxic, can cause eye irritation, skin rashes, mouth ulcers, vomiting, diarrhoea, and cold or flu-like symptoms. Drinking or swallowing the water can be dangerous.

“It is important to note that Rietvlei is at the lower reach of a highly urbanised catchment and experiences periods where water quality is not safe for recreation,” said Ms Nieuwoudt.

Pollution from a “myriad” sources, including stormwater run-off from urban areas, entered Rietvlei to “exacerbate” the algae blooms, said Ms Nieuwoudt.