Milnerton Lagoon Environmental Report - 31 Oct. 2026
Milnerton Lagoon and the Diep River: Status Report
1. Key Findings
- Official indicators are moving the right way. Nuisance-odour exceedances fell from 1,397 in 2025 to 10 in the first quarter of 2026, sewer blockages are down, and Potsdam Wastewater Treatment Works (WWTW) has recorded a first fortnight of 100% effluent compliance (City of Cape Town, 2026a, 2026b).
- Signs of life are returning. The City reports lighter, sandier sediment, better oxygen levels and Southern mullet caught high up the river (Isaacs, 2026; City of Cape Town, 2026b).
- The Potsdam upgrade is about 80% complete. Its membrane bioreactor is installed and commissioning is due before the end of the year, with full completion in 2027 (Engineering News, 2026).
- Two big lagoon interventions are still ahead. A beach-well pilot began in September, while dredging awaits the outcome of eight appeals and is not expected before early 2027 (Staff Reporter, 2026; City of Cape Town, 2026b).
- Caution is warranted. Most of the good news comes from the City, improvement has been helped by rain, and I found no recent independent E. coli results for the lagoon itself that confirm the trend.
2. The Lagoon in Context
Milnerton Lagoon is the lower end of the Diep River estuary, a system of roughly 900 hectares that also takes in the Rietvlei wetland. Its flow is shaped by seasonal river inflows and, importantly, by treated effluent from Potsdam WWTW. More than half of the river's catchment is farmland, and a significant part lies outside the City of Cape Town's jurisdiction (Western Cape Government, 2021). Pollution reaching the lagoon therefore has several sources, but for years residents, scientists and the provincial regulator have pointed to Potsdam and the leaking, overloaded sewers feeding it.
The low point is well documented. In September 2020 the provincial environmental law-enforcement directorate, the Green Scorpions, issued a directive ordering the City to remedy the Diep River and the lagoon (Organisation Undoing Tax Abuse [OUTA], n.d.). The national limit for E. coli in discharged wastewater is 1,000 colony-forming units (cfu) per 100 ml (Human, 2020), yet independent tests in November 2022 recorded effluent leaving Potsdam at 750,000 cfu per 100 ml (Sowetan, 2022). As recently as May 2025, the community group RethinkTheStink reported 1.3 million cfu per 100 ml at the Wooden Bridge, the same month the Western Cape MEC reportedly granted the City a further three years to finish overdue upgrades (Serra, 2025).
It is against that backdrop, and not against a pristine baseline, that the improvements of 2026 should be read.
3. How to Use This Report
Section 1 gives the five headline findings and section 2 the background. Sections 4 to 7 cover what has improved, the Potsdam upgrade, the catchment and the lagoon itself. Section 8 explains why caution is warranted, section 9 sets out the expected milestones, and section 10 is a tick-box table of the measures to watch. Section 11 describes the method and its limits.
Milnerton Lagoon: A New Chapter in Its Restoration
Milnerton Lagoon: A Coastal Landscape in Transition
Milnerton Lagoon: Environmental Health Boost
4. What Has Improved
Odour and air quality
The clearest numbers come from hydrogen sulphide (H2S) monitoring, which began in February 2025. Between 26 February and 31 December 2025 the monitors logged 1,397 exceedances of the World Health Organization's 30-minute nuisance guideline. From 1 January to 26 March 2026 there were only 10. The WHO's daily health-based guideline has not been exceeded at any point since monitoring started (City of Cape Town, 2026a, 2026b). The City says the drop reflects better wastewater management and fewer pollution incidents.
Sewer network and pump stations
City data show blockages across the catchment fell from 4,270 in October 2024 to 3,489 in February 2026, a drop of about 18% (Swart, 2026). More than 31 kilometres of sewer pipe were proactively cleaned in 2025/26, and telemetry now monitors all 56 pump stations in the Potsdam catchment in real time (City of Cape Town, 2026b). At the Koeberg Road pump station, long one of the worst trouble spots, new sand traps and mechanical screens have brought what the City's engineering manager described as significant improvement (Isaacs, 2026). When the Racecourse pump station's rising main collapsed in June 2026, vacuum tankers and manual operation limited the damage while repairs were finished within two days (City of Cape Town, 2026b).
Potsdam's effluent
At a public meeting on 24 June, the City's bulk services director reported overall effluent compliance of around 80% across the two most recent sampling periods, with E. coli still above limits while a new discharge pipeline was being installed. He expected full compliance by late July or early August (Isaacs, 2026). By 8 July the City announced that Potsdam had achieved two consecutive weeks of 100% compliance across all measured final-effluent parameters. It cautioned that performance would still vary during construction, and that sustained compliance is expected only once all new infrastructure works together as one system (City of Cape Town, 2026b). I could not find compliance figures for the period since July.
Signs of ecological recovery
The City's environmental manager told residents the lagoon had shown “slow but gradual improvement” over two months, partly thanks to autumn and early-winter rain. Sediment samples no longer showed the black, oxygen-starved conditions recorded earlier; the material is now sandier and lighter, particularly in the upper reaches. The mouth of the lagoon, he said, is working better than before (Isaacs, 2026). The City's July statement added that higher dissolved oxygen and the capture of a Southern mullet far up the Diep River point to improving conditions, which it called an early milestone in a long journey (City of Cape Town, 2026b).
| Indicator | Earlier position | Latest reported position | Source |
|---|---|---|---|
| Nuisance odour exceedances (H2S) | 1,397 (26 Feb–31 Dec 2025) | 10 (1 Jan–26 Mar 2026) | City of Cape Town (2026a) |
| Sewer blockages in catchment | 4,270 (Oct 2024) | 3,489 (Feb 2026) | Swart (2026) |
| Potsdam effluent compliance | About 80% (two sampling periods to June 2026) | 100% for two consecutive weeks (reported 8 July 2026) | Isaacs (2026); City of Cape Town (2026b) |
| Sediment condition | Black, oxygen-depleted | Sandier, lighter, especially upstream | Isaacs (2026) |
| Marine life | Fish die-offs in earlier years | Southern mullet caught high up the Diep River | City of Cape Town (2026b) |
Table 1. Selected improvement indicators reported for the lagoon and catchment. All figures are City-reported.
5. The Potsdam Upgrade
Potsdam is the pivot on which the lagoon's recovery turns. Construction on the R5.2-billion upgrade began in 2023, after more than a decade of delays caused by bidder appeals, with the aim of doubling capacity from 47 to 100 million litres a day and adding membrane technology (Engineering News, 2023). The Mayor said at the time that the upgrade would be dovetailed with lagoon dredging in around two years. That sequencing has slipped, but the plant itself has advanced steadily.
By September 2025 the project was 60% complete, the ultrafiltration plant had entered a 12-month trial from June, the dewatering plant had been running since May, and the treated-effluent pump station for reuse was finished (City of Cape Town, 2025). Reporting on 21 October 2026 put overall progress at 80%, with a 65-million-litre-a-day membrane bioreactor installed and, in the Mayor's words, on track for commissioning later this year ahead of full completion next year. The new inlet works and raw-sewage pump station are already being commissioned (Engineering News, 2026). The City has said the membrane bioreactor will significantly improve nutrient removal and effluent quality (City of Cape Town, 2026a).
6. The Catchment: Where the Next Gains Lie
The treatment works can only perform if the network feeding it stops leaking raw sewage. Table 2 summarises the pump-station programme as the City described it in 2026. It also shows how schedules have shifted, which matters for anyone tracking delivery.
| Pump station | Status reported | Timing |
|---|---|---|
| Koeberg Road | Sand trap and screens commissioned; overflows contained. Procurement under way for a new high-capacity pump station. | Replacement: not yet scheduled |
| Du Noon | Screen upgrades and overflow improvements. | Target moved from June 2026 (April) to October 2026 (July) |
| Phoenix | Highest infrastructure priority because of its failure rate. Conceptual design stage. | Construction anticipated October 2028, subject to approvals |
| Table View East | Overflow pond recommissioned; basket screen and fourth standby pump being installed. | Larger upgrade to follow |
| Sanddrift East | Planning for a major upgrade; construction reported as due to start soon. | Not confirmed |
| Joe Slovo | Now needs a complete upgrade after illegal stormwater connections were found straining the sewer. | Not confirmed |
Table 2. Pump-station programme. Sources: City of Cape Town (2026a, 2026b); Isaacs (2026).
7. The Lagoon Itself: Beach Wells and Dredging
Beach-well pilot
Drilling of beach wells at Milnerton Beach began on 16 September 2026 and was expected to last about two weeks. The pilot will test whether saline groundwater pumped into the upper lagoon can improve flushing, dilute pollutants and raise dissolved oxygen and salinity. Water was due to be added from early October, followed by a six-month trial, after which the City will decide whether to continue, modify or discontinue the scheme. It is being implemented under a Section 28(4) directive of the National Environmental Management Act (Staff Reporter, 2026). In April the City said the pilot would introduce 80 to 100 litres per second (City of Cape Town, 2026a). I could not confirm whether pumping had started by the end of October.
Dredging
In 2024 the City settled on a plan to dredge a key channel and use cyclone technology to separate organic material from sand, returning clean sand to the lagoon. About 600 cubic metres of organics and sediment would be disposed of, at a projected cost of around R70 million over 11 months (City of Cape Town, 2024). By April 2026 a tender was under evaluation with work expected from June, covering a defined channel, reshaped sandbanks, a berm and management of the lagoon mouth (City of Cape Town, 2026a).
That date has not held. Environmental authorisation has been granted, but eight appeals were lodged against it. A decision is expected later in 2026, procurement will resume once the appeals are settled, and dredging is now expected in early 2027 if the authorisation is upheld (City of Cape Town, 2026b). The scheme is also contested locally. Some residents asked at the June meeting whether it was still necessary now that river flows were improving conditions, and others feared an “ugly outcome”; the City said rain had already flushed much accumulated sediment, but it still intends to dredge sections to about one metre (Isaacs, 2026).
8. Reasons for Caution
Four caveats run through the evidence. First, the improvement is largely documented by the City. The independent monitoring that exposed the crisis, from OUTA and RethinkTheStink, has not, in the sources I could find, produced 2026 lagoon E. coli results to set beside the City's compliance claims. Second, rainfall helps: both the City and residents acknowledge that winter flows flushed sediment and raised oxygen, so the dry summer ahead is the real test. Third, Potsdam's own officials expect compliance to fluctuate until every new unit is commissioned. Fourth, schedules keep moving, as the Du Noon and dredging dates show, and the 2025 extension of the provincial deadline means regulatory pressure is softer than it was.
Residents nonetheless sound hopeful. Several told the June meeting they felt there was finally “light at the end of the tunnel” after more than 14 years of decline (Isaacs, 2026).
9. The Way Ahead
| When | Milestone | Status / source |
|---|---|---|
| October 2026 | Du Noon pump station screen and overflow upgrades complete | Targeted in July (City of Cape Town, 2026b) |
| Early October 2026 onward | Beach-well pilot begins adding water; six-month evaluation follows, ending roughly April 2027 | Planned (Staff Reporter, 2026); start unconfirmed |
| November 2026 | Potsdam membrane bioreactor commissioning | Targeted in April (City of Cape Town, 2026a); “later this year” in October (Engineering News, 2026) |
| Late 2026 | Decision on eight appeals against dredging authorisation | Expected (City of Cape Town, 2026b) |
| Early 2027 | Dredging begins, if authorisation upheld and procurement resumes | Expected (City of Cape Town, 2026b) |
| 2027 | Full completion of Potsdam upgrade: 100 million litres a day | Stated by Mayor (Engineering News, 2026) |
| October 2028 | Phoenix pump station construction anticipated | Subject to approvals (City of Cape Town, 2026a) |
Table 3. Key milestones. Dates are the City's own and have moved before.
10. What to Watch
Five measures will show whether the gains are real. If all five move the right way, the lagoon's recovery will rest on evidence rather than on rainfall and optimism.
| Tick | Measure | Why it matters |
|---|---|---|
| ☐ | Potsdam final-effluent compliance | Especially E. coli, once the membrane bioreactor starts. The City expects sustained compliance only when all new infrastructure works together. |
| ☐ | Independent E. coli sampling | Lagoon results through the dry summer would test the City's figures, since rain has helped so far. |
| ☐ | Odour monitoring | Hydrogen sulphide exceedances against the 2025 baseline of 1,397. |
| ☐ | Beach-well trial data | Oxygen, salinity and flushing results will decide whether the pilot continues, changes or stops. |
| ☐ | Dredging appeals | The outcome of the eight appeals decides whether dredging can start in early 2027. |
11. Method and Limits
This report draws on City of Cape Town media statements, community and national press reports and provincial documents available at 31 October 2026. Two pages, Engineering News (2026) and Cape Argus (2026), blocked full retrieval, so I relied on the text visible in search excerpts for those. Figures are as reported by the cited sources and have not been independently verified. Anyone relying on the numbers for decisions should check them against the City's current statements.
12. References
Cape Argus. (2026, October 8). City blames muddy sediment for discoloured water entering Milnerton Lagoon. IOL. https://iol.co.za/capeargus/news/2026-10-08-city-blames-muddy-sediment-for-discoloured-water-entering-milnerton-lagoon/
City of Cape Town. (2024, September 5). Interventions on track to improve Milnerton Lagoon's water quality. https://www.capetown.gov.za/Media-and-news/Interventions%20on%20track%20to%20improve%20Milnerton%20Lagoon%27s%20water%20quality
City of Cape Town. (2025, September 23). Potsdam wastewater plant upgrade reaches 60% mark. https://www.capetown.gov.za/Media-and-news/Potsdam%20wastewater%20plant%20upgrade%20reaches%2060%20mark
City of Cape Town. (2026a, April 1). City perseveres with interventions to restore Milnerton Lagoon. https://www.capetown.gov.za/media-and-news/city-perseveres-with-interventions-to-restore-milnerton-lagoon/
City of Cape Town. (2026b, July 8). Milnerton Lagoon shows improved water quality. https://www.capetown.gov.za/Media-and-news/Milnerton%20Lagoon%20shows%20improved%20water%20quality
Engineering News. (2023, August 2). Potsdam wastewater works upgrade breaks ground. https://www.engineeringnews.co.za/article/potsdam-wastewater-works-upgrade-breaks-ground-2023-08-02
Engineering News. (2026, October 21). R5.2bn Potsdam wastewater upgrade reaches new milestone. https://engineeringnews.co.za/article/r52bn-potsdam-wastewater-upgrade-reaches-new-milestone-2026-10-21
Human, L. (2020, December 8). High levels of E. coli in water from Milnerton waste plant, say activists. GroundUp. https://groundup.news/article-print/milnerton-waste-plant-discharges-effluent-high-levels-ecoli-says-activists
Isaacs, T. (2026, June 25). Milnerton Lagoon shows signs of recovery, residents express cautious optimism. Table Talk. https://tabletalk.co.za/news/2026-06-25-milnerton-lagoon-shows-signs-of-recovery-residents-express-cautious-optimism/
Organisation Undoing Tax Abuse. (n.d.). Enough is enough on Milnerton pollution. https://www.outa.co.za/blog/newsroom-1/enough-is-enough-on-milnerton-pollution-1074
Serra, G. (2025, May 19). Extension granted to fix 'stinky' Milnerton Lagoon. Cape Argus. https://capeargus.co.za/news/2025-05-19-extension-granted-to-fix-stinky-milnerton-lagoon/
Sowetan. (2022, November 24). 'Stinky' Cape Town wastewater treatment plant to get R5bn upgrade. https://www.sowetan.co.za/news/south-africa/2022-11-24-stinky-cape-town-wastewater-treatment-plant-to-get-r5bn-upgrade/
Staff Reporter. (2026, September 17). City starts drilling wells at Milnerton Beach to improve lagoon water quality. Table Talk. https://tabletalk.co.za/news/2026-09-17-city-starts-drilling-wells-at-milnerton-beach-to-improve-lagoon-water-quality/
Swart, M. (2026, April 15). Milnerton Lagoon shows early signs of recovery. Cape Argus. https://www.capeargus.co.za/news/2026-04-15-milnerton-lagoon-shows-early-signs-of-recovery/
Western Cape Government. (2021). Diep River estuary management protocol. https://www.westerncape.gov.za/eadp/sites/eadp.westerncape.gov.za/files/atoms/files/Diep_River_EMP_FINAL.pdf
