The City of Cape Town has advised the public that contrary to what has been reported the naturally-occurring algal blooms along False Bay’s coastline are non-toxic and unrelated to inland waste or water quality.
The National Department of Agriculture Forestry and Fisheries (DAFF) has identified the species of algae as Lepidodimium chloroforum. DAFF is responsible for monitoring the occurrence of algal blooms and for issuing any consumer warnings in the event of a toxic algal bloom, or ‘red tide’.
Algal blooms occur when there is an ocean upwelling, a phenomenon which brings colder, nutrient-rich water and dinoflagellate cells (a subgroup of algae) towards the water’s surface. The combination of nutrients, warmth and sunlight make for ideal conditions for the cells to bloom into algae.
Five of the 10 Cape Town Blue Flag Beaches are in False Bay, between Fish Hoek and Bikini Beach. The water quality of a beach must meet certain high standards before the beach can achieve Blue Flag status.
Impacts of the algal bloom on:
Desalination plants
The City says statements that its desalination plants have not been working due to a functional failure or ‘cover-up’ are not true.
The halted operations at the Strandfontein and Monwabisi desalination plants, the City says, are actually a precautionary measure due to the presence of algal blooms and high turbidity in the ocean (which is caused by strong winds and big ocean swells) in the two areas.
Algal blooms damage the sensitive membrane filtration systems at desalination plants, while high turbidity hinders the pre-treatment process, meaning the plants should not be operated in such conditions. The City continues to monitor and conduct technical assessments on the plant.
The City’s official statement reads, “Both plants … stopped producing drinking water on 16 November 2018 due to the occurrence of the algal bloom but are fully functional otherwise.”
Operations are continuing again at the Strandfontein plant as the algal bloom has dissipated from the area, while Mowabisi is expected to go back into operation soon when conditions allow it.
Zandvliet Waste Water Treatment Plan (WWTP) upgrades
The algal bloom has affected the inland waste water treatment upgrades for the Zandvliet Plant. In an effort to mitigate the environmental impact, 8-million litres per day of flow into the Zandvliet WWTP is being diverted to the Bellville WWTP.
Picture: City of Cape Town