A University of Cape Town scientist and a residents’ group have raised concerns about a R15 million City of Cape Town plan to clean up the Milnerton Lagoon. They said the plan dilutes the pollution but does not stop it at the source, GroundUp reported.
The pilot project pumps salty groundwater from the beach into the upper lagoon. The aim is to raise oxygen and salt levels and flush pollution out to sea.
“Dilution of pollution is not the solution,” said UCT professor Kevin Winter.
Winter called the project a “bold experiment”. He said it does not deal with where the pollution comes from. He also said the sea would once again receive the pollution.
Winter said the city’s water quality data show some improvement since 2024. There are fewer bacteria and lower levels of ammonia, nitrogen, phosphorus and chlorophyll.
“There is evidence of some improvements in 2026 and in some instances, the lagoon water quality at Woodbridge Island Bridge is getting closer to the better-quality water that was evident in 2018,” he said.
The lagoon has been badly polluted for years. Most of the pollution comes from poorly treated effluent from the Potsdam Wastewater Treatment Works.
The works releases more than 40 million litres of effluent a day into the Diep River, about 5km upstream of the lagoon. According to the Department of Water and Sanitation, Potsdam has failed national effluent standards since 2018.
Other sources include stormwater from the Joe Slovo informal settlement and the Montague Gardens industrial area. Sewer pipe collapses, pump station overflows and fertiliser from farms also add to the problem.
Caroline Marx heads the environment portfolio of the Milnerton Central Residents Association and Rethinkthestink. She said it is too early to celebrate.
“In 2026, there have been repeated serious sewage pollution events, with Potsdam Wastewater Treatment Works again releasing tens of millions of litres per day of shockingly poor-quality effluent despite years of assurance that performance was improving,” said Marx.
On 8 September, E. coli at Woodbridge was measured at 141 000 cfu/100ml. Levels must be below 4 000 cfu/100ml for canoeing to be safe. The levels stayed above this limit for at least a month.
The latest reading, on 20 October, showed 1 600 cfu/100ml, which is rated an acceptable risk. But nitrogen, ortho-phosphate and un-ionised ammonia were still at unacceptable levels.
In September, deputy mayor Eddie Andrews said water would be added to the lagoon in early October. A six-month trial would follow, with close monitoring of water quality. He said the results would show if the project should continue, change or stop.
Andrews told GroundUp that the lagoon is a tidal system and already has salty water far upstream. He said the pilot takes these conditions into account.
Mayco member for water and sanitation Zahid Badroodien said the pilot “does not detract from the City’s substantial investment in wastewater infrastructure, including the R5.2 billion upgrade of the Potsdam Wastewater Treatment Works”.
In October, new membrane bioreactor filters that can treat 65 million litres a day were installed at Potsdam. The City said the upgrade was 80% complete.
Mayor Geordin Hill-Lewis said the upgrade will raise the plant’s capacity from 47 to 100 million litres a day. He said the full upgrade will be finished next year.
Marx said other projects, such as the Phoenix Pump Station upgrade, must be sped up. She also raised worries about a plan to dredge the lagoon.
In July, the City said dredging had been approved but eight appeals had been lodged. If the approval is upheld, dredging is expected to start in early 2027, the City said.
Source: this article is based on reporting by Moneyweb. Image: Moneyweb. Written with the help of AI and published by the Tzaneen Voice Business desk. See our Editorial Standards.
Anelisa Nkuna covers business and money news for Tzaneen Voice. Anelisa reports on the rand, fuel prices, interest rates, jobs, Eskom, Transnet, farming and company results. The aim is simple: explain what the numbers mean for household budgets, small businesses and workers in South Africa.