Toxic algae in Rietvlei sank a popular endurance sailing challenge.
The City of Cape Town closed the vlei to recreational activities after the blue-green algal bloom was spotted on Thursday March 16.
As a result, the Milnerton Aquatic Club’s 24-hour endurance sailing challenge, scheduled to take place at the weekend was cancelled.
Julia Wood, from the City’s environmental resource management department, said water samples last week revealed toxins associated with blue-green algae exceeded the World Health Organisation’s guidelines.
The algal blooms are typically seen as green, blue-green, white or brown foam, scum or mats floating on the surface of the water.
Exposure to these algae can cause eye irritation, skin rashes, mouth ulcers, vomiting, diarrhoea, and cold or flu-like symptoms. Drinking or swallowing large amounts of water can be extremely dangerous.
The City has advised the public to stay out of the water at Rietvlei until it has been declared safe.
Due to the ongoing drought and low water levels there are extensive areas of exposed dry shoreline around Rietvlei and it is suspected that the 5mm rainfall recorded last Wednesday, March 15, washed accumulated minerals and organic material from decomposing and dead plants along the shoreline into the water.
Together with high ambient temperatures, it could have provided the nutrients for the rapid growth of algae in the water.
The City is monitoring the water quality and will inform the public once it is safe for recreational use, including fishing.
The closure does not prevent anybody from accessing the Table Bay Nature Reserve’s other visitor facilities such as the picnic areas, braai facilities and the bird watching trail.