The City of Cape Town would like to advise residents and visitors to the presence of toxic blue-green algae in the Wildevoelvlei in Noordhoek Valley. The public are therefore advised to avoid contact with this body of water.
Wildevoelvlei has a well-established algal population, dominated by species of blue-green algae (Cyanophyceae). This algal group has the ability, under certain conditions, to produce toxins which can be harmful to humans and animals if ingested. During the warm summer months, the algal population can increase dramatically and this productivity accounts for the green pea-soup colour of the water. Residents and visitors may have noticed that the Wildevoelvlei is currently a distinct green colour. Recent monitoring and laboratory tests undertaken by the City have confirmed that the water contains blue-green algal toxins.
The public should avoid all contact with the water at the vlei and in the outlet channel leading to the sea. It has been established that the vlei had an outbreak which affected water flowing downstream and discharging on a section of Noordhoek Beach. Dog-walkers should ensure that their pets remain on their leashes so that they are not able to drink the water.
Harvesting, sale and consumption of shellfish from the rocky outcrops near the outlet to the sea (Klein Slangkop on Noordhoek Beach) is not advised. Shellfish such as mussels harvested from this area are likely to be unfit for human consumption as a result of the toxins.
The algal blooms usually present as green, blue-green, white or brown foam, scum or mats floating on the surface of the water. Exposure to this algae can cause eye irritation, skin rashes, mouth ulcers, vomiting, diarrhoea, and cold or flu-like symptoms. Drinking or swallowing large amounts of contaminated water can be extremely dangerous.
If any person comes into direct contact with the blue-green algae, they should wash themselves immediately with clean water. If any symptoms present, they should immediately seek medical advice.
The City’s Environmental Health officials are in the process of erecting additional signage at various locations to warn the public of the situation. The City will continue to monitor the water quality of the vlei carefully and will keep the public informed of any new developments. Water samples from the vlei are assessed regularly as part of the City’s Water Quality Monitoring Programme. The City will remove the warning signs on the beaches once the vlei is clear of all potential health risks.
In the past, large quantities of salt were deposited into the Wildevoelvlei in an attempt to eradicate a toxic bloom a few years ago. This was successful in breaking the particular blue-green algae bloom cycle, but the success was short-lived. The Wildevoelvlei has, in the ensuing years, become dominated by blue-green algae year-round. It is unlikely that the City will conduct another ‘salt-bombing’ because the National Environmental Management Act and the National Water Act require that a detailed assessment be conducted to obtain authorisation for such an intervention. The possibility of opening the mouth of the vlei to improve flushing and to encourage natural salt water intrusion from the sea is being explored with the relevant authorities.
If any member of the public requires more information on this matter, they should contact the Lakeside Environmental Health Office on 021 788 9350
COMMUNICATION DEPARTMENT, CITY OF CAPE TOWN
DR. VIRGINIA DE AZEVEDO
ACTING EXECUTIVE DIRECTOR: CITY HEALTH
CELL: 083 629 3344