The City of Cape Town informed members of the public to avoid all contact with the water at the Wildevoelvlei and outlet channel leading to the sea. Wildevoelvlei had a well-established algae population dominated by species of blue-green algae named Cyanophyceae.
During the warm summer months, the algal population could increase dramatically, and this accounted for the current green pea-soup colour of the water.
Shellfish such as mussels harvested from the coast below the vlei were likely to be unfit for human consumption as a result of the toxins. Exposure to the algae could cause eye irritation, skin rashes, mouth ulcers, vomiting, diarrhoea, and cold or flu-like symptoms. Drinking or swallowing large amounts of contaminated water could be extremely dangerous.