The City of Cape Town has blamed rapid algae growth in the sewage-polluted estuary for the second fish die-off in the Milnerton lagoon this year.
This is according to City spokesperson, Luthando Tyhalibongo, who said that while an exact cause still had to be confirmed, depleted oxygen levels caused by algae growth was the likely culprit.
“Nutrient loading that has built up in the system over many years is also a significant problem,” he said.
Tyhalibongo explained that the City’s nature reserve staff and pollution control staff went to the lagoon to take water quality samples on 8 October and noticed that the fish had been affected.
A draft of the Diep River Estuary Management Plan, outlining the City’s priorities to tackle the pollution issues in the estuary, the Diep River, which flows into the Milnerton lagoon, has suffered prolonged pollution from the Potsdam wastewater treatment works. The draft plan, which still needs to be finalized, describes the E. coli as “high and increasing.”
The City is planning to upgrade the failing Potsdam works and the upgrade of R2.2 billion will be complete by 2026. Tenders for these upgrades were closed earlier this year.
Meanwhile, spokesperson for the Organization Undoing Tax Abuse, Ferrial Adam said that the upgrades would take too long and low quality effluent would continue to be discharged into the Diep River until 2026.
Adam said that the City had no clear timeline for action being taken following the directive issued by the Green Scorpions in 2020, ordering the City to clean up the pollution
An audit by the Green Scorpions in December indicated that the City was meeting only five of 16 conditions.
The OUTA spokesperson added that during a site visit to the Diep River estuary at the end of September City officials had said the effluent quality should be improving, but the fish die-off had shown that this is not the case.
The draft plan outlines the City’s priorities for improving water quality and managing the declining ecological state of the estuary.
It notes that water quality in the Diep River has declined due to a number of things: low quality effluent from Potsdam, sewer spills from pump stations, urban run-off from stormwater drains, and informal settlements upstream. In 2020, there were 122 000 sewer spills in the Diep River.
Tyhalibongo said that the City is committed to resolving the issues in the Diep River and Milnerton Lagoon but that there are “no quick or single solutions”.