Date: 1 October 2025: Milnerton Lagoon and Woodbridge Island face a multi-faceted pollution challenge dominated by sewage and compounded by stormwater, infrastructure constraints and legacy issues.
Executive summary
Milnerton Lagoon and the adjacent Woodbridge Island remain subject to persistent and multi-source pollution in 2025. The dominant and recurring problem is untreated or partially treated sewage reaching the Diep River and Milnerton Lagoon (affecting the lagoon mouth, adjacent beaches and nearby coastal waters). This has generated recurring high bacterial loads, foul hydrogen sulphide (H₂S) odours, toxic algal/organic decomposition events, and periodic beach closures and public-health advisories. Infrastructure failures (notably at the Potsdam Wastewater Treatment Works), inadequate stormwater management, runoff from informal settlements, and legacy marine outfalls are the main drivers. Local government has implemented a mix of short-term monitoring (including temporary air-quality stations) and longer-term infrastructure upgrades, but community groups and independent testing campaigns continue to report concerning results and demand faster remedial action. This report documents the state of the system, identifies primary pollution sources and impacts, evaluates recent interventions, and gives prioritized recommendations for immediate and medium-term action. (GroundUp News)
1. Background and geographic contextMilnerton and Woodbridge Island lie on Cape Town’s western seaboard. The Milnerton Lagoon (the lower reach of the Diep River estuary) connects to the Atlantic near Woodbridge Island and forms part of the Table Bay Nature Reserve. The lagoon and adjacent beaches (including Lagoon Beach and the coastline off Woodbridge Island) are used for recreation (walking, kite surfing, water sports) and support estuarine biodiversity; they are also adjacent to dense urban development and transport corridors, which influence pollutant inputs. (Cape Town Government)
2. Summary of the pollution problem (current status — 2024–2025)- 2.1 Sewage and wastewater-related contamination
Multiple investigative and media sources in 2024–2025 indicate that treated and untreated sewage is the single largest contributor to water quality degradation in the Diep River—Milnerton Lagoon system. Failures or capacity shortfalls at the Potsdam Wastewater Treatment Works (WWTW) have been repeatedly flagged; the plant discharges into the river system upstream of the lagoon, and when treatment is inadequate the result is elevated bacterial counts, organic loading and visible pollution in the lagoon and along the coast. Local investigative reporting and NGO testing have found evidence of raw or poorly treated sewage entering waterways, and community groups report frequent overflows and foul odour events. (GroundUp News)
- 2.2 Hydrogen sulphide (H₂S) and air-quality nuisance
Residents and visitors have reported persistent sewer stench and episodes of foul-smelling air over Milnerton and Woodbridge Island. The City of Cape Town has responded by installing temporary mobile ambient air-quality monitoring stations to measure hydrogen sulphide (H₂S) and other parameters, after which limited pilot mitigation steps (e.g., bioremediation trials) were announced. The use of temporary monitoring followed damage or vandalism to earlier H₂S monitoring equipment and public pressure to track odour events. (Table Talk)
- 2.3 Stormwater, runoff and informal settlement impacts
Urban stormwater carries litter, hydrocarbons, nutrients and faecal contamination from diffuse sources into drains that feed the Diep River system. Informal settlements and aging sewer networks contribute intermittent raw sewage to the system, especially during high-flow or system-failure events. These diffuse contributors exacerbate the impact of point-source treatment failures, producing episodic spikes in bacterial indicators. (WaterCan)
- 2.4 Marine outfalls and coastal receiving water concerns
Cape Town operates marine outfalls that discharge partially treated effluent offshore; the city has acknowledged permit violations at times and debates continue about the extent to which ocean discharges affect nearshore beach water quality. The proximity of outfalls, tidal exchange and lagoon mouth dynamics interact to determine whether pollution remains local to the lagoon or is dispersed along the coast. (The Guardian)
- 3.1 Public health risks
Sewage contamination elevates risk of gastrointestinal illness, skin infection and other exposures for people using lagoon waters, beaches and recreational waters. Citizen testing groups and local media reporting have repeatedly recorded elevated bacterial indicators (e.g., enterococci and E. coli) at times, prompting closures or advisories in the broader Cape Town context. H₂S exposure at high concentrations can cause acute irritation and annoyance and reduces quality of life for residents. Vulnerable populations (children, elderly, immunocompromised) are at highest risk. (The Guardian)
- 3.2 Ecological effects
- Chronic organic loading reduces dissolved oxygen, stresses fish and invertebrates, and promotes opportunistic algal growth and decomposition events. Estuarine habitat complexity (salt marshes, mudflats) can be degraded by sedimentation and contaminant load, affecting birds and nursery habitats. Persistent pollution also undermines ecosystem services and the conservation value of the Table Bay Nature Reserve. (Cape Town Government)
- 3.3 Social and economic consequences
Repeated pollution incidents reduce amenity value, affect tourism and local property perceptions, restrict sports and youth water programs (e.g., canoe/kayak development programs), and impose economic costs for the municipality and affected businesses. Community activism and reputational effects of high-profile pollution stories (national press and international coverage) add political pressure but also raise community anxiety. (The Guardian)
- Potsdam Wastewater Treatment Works (WWTW) — chronic operational and capacity issues at this facility upstream of the Diep River are repeatedly cited as a key driver. When the WWTW under-performs, raw or poorly treated effluent enters the river and flows downstream to the lagoon. (GroundUp News)
- Sewer network failures and informal settlement sanitation — combined sewer blockages, overflows and inadequate sanitation services in some areas feed untreated sewage into storm drains and watercourses, especially during heavy rains. (WaterCan)
- Urban stormwater runoff — diffuse pollution from roads, commercial areas and residential neighbourhoods transports heavy metals, oils, nutrients and litter to the lagoon via drainage systems. (Cape Town Government)
- Marine outfalls and managed discharges — the city’s marine outfalls discharge partially treated effluent offshore and contribute to coastal contamination patterns during certain conditions, although far-field dilution is a factor. (The Guardian)
- Legacy contamination and sediment mobilisation — historical discharges and sediment-bound pollutants can be resuspended during storms or dredging, prolonging contamination even after inputs are reduced. (Local monitoring data are limited; sediment surveys would clarify this driver.) (Cape Town Government)
- 5.1 City of Cape Town responses
The City has publicly reported a range of interventions: upgrades to wastewater infrastructure (a multi-year capital program), the deployment of a temporary ambient air-quality station to monitor H₂S at Woodbridge Island, valve adjustments and hydraulic interventions in the lagoon system, and trial bioremediation measures. The City also emphasizes investment across wastewater projects (multi-billion rand programs). These initiatives indicate intent but community stakeholders remain skeptical about delivery timelines and interim protections. (Cape Town Government)
- 5.2 Independent monitoring and civil society
Activist and citizen science groups (notably Rethink the Stink and associated local campaigns) have conducted independent water testing and public reporting, challenging official assurances and producing data that indicate high bacterial loads at times. NGOs and community groups have also used media and Council processes to escalate the issue. (The Guardian)
- 5.3 Media and investigative reporting
Local and national news outlets (GroundUp, Mail & Guardian, The Guardian, Table Talk and local blogs/photographers) have documented smell events, reported on the operational status of Potsdam WWTW, and covered community protests and council debates. This coverage has heightened public awareness and shaped political responses. (GroundUp News)
- Comprehensive, high-frequency water quality data for the Diep River–Milnerton Lagoon continuum are limited in the public domain, making it difficult to quantify temporal patterns, source apportionment and compliance with national microbial standards across seasons. Independent testing exists but is geographically and temporally patchy. (WaterCan)
- Sediment contamination studies are scarce; without sediment profiles it is difficult to know how much legacy contamination contributes to observed impacts. (Cape Town Government)
- Health outcome data linkage (confirmed illness attributable to lagoon/beach exposure) is sparse; syndromic surveillance or hospital-ED data linked to exposure events would strengthen risk assessments.
- Longitudinal effectiveness data for the City’s pilot bioremediation and air monitoring projects are limited publicly; independent evaluation is needed to confirm efficacy. (Table Talk)
- Public-health protective actions: issue regular, clearly signposted advisories when independent or municipal testing indicates elevated bacterial counts or H₂S exceedances; proactively close access to high-risk recreational areas until safe thresholds return. Ensure rapid public notification via local channels. (GroundUp News)
- Rapid source-control emergency repairs: prioritize troubleshooting and immediate fixes at Potsdam WWTW to stop raw effluent releases (pump failures, bypasses, blockages). Deploy mobile containment and bypass treatment units if full plant remediation will be delayed. (The Mail & Guardian)
- Expand monitoring footprint: supplement the existing temporary H₂S station with high-frequency bacterial testing at the lagoon mouth, selected beaches, and upstream Diep River points. Publish data in real time on an accessible dashboard. Citizen science groups should be formally integrated into monitoring networks with quality control. (Table Talk)
- Immediate odour mitigation: where H₂S is acute, use temporary aeration, floating booms with adsorbents and targeted desludging to reduce anaerobic decomposition hotspots while upstream flows are controlled. (Table Talk)
- Accelerate infrastructure upgrades: fast-track capital works at Potsdam WWTW and prioritize sewer network rehabilitation in critical catchments. Reassess the City’s delivery timelines and, where necessary, contract additional resources to avoid multi-year slippage. Transparency on milestones is essential. (Cape Town Government)
- Stormwater source control and SUDS: implement green infrastructure (swales, retention basins, constructed wetlands) in key subcatchments to trap solids, reduce pollutant loads and attenuate storm surges that carry contaminants to the lagoon. (Cape Town Government)
- Revisit marine outfall management: assess discharge permits, monitoring of nearshore receiving waters and consider advanced treatment or staged outfall redesign where evidence shows local impacts. Increase monitoring of coastal transects during discharge events. (The Guardian)
- Community engagement and sanitation upgrades: work with affected communities (including informal settlements) to provide onsite sanitation solutions where sewer service is absent or unreliable; remove illegal connections and provide recycling/education programs to reduce illegal dumping. (WaterCan)
- Integrated catchment management plan: develop and implement an integrated Diep River–Milnerton Lagoon catchment plan that combines wastewater capacity, stormwater management, land-use planning, biodiversity restoration and public access management, driven by clear targets and independent performance audits. (Cape Town Government)
- Restoration of estuarine habitats: restore salt marshes and reedbeds where feasible to improve natural filtration and habitat value; undertake sediment remediation where hotspot legacy contamination is documented. (Cape Town Government)
- Independent oversight and transparent reporting: establish an independent technical advisory panel (including local scientists, public health experts and community representatives) to audit progress, validate monitoring data and report publicly on milestones. (The Guardian)
- Funding & procurement: capital upgrades are costly—municipal budgeting should be aligned with provincial and national support programs, and procurement should prioritize speed and technical quality. Public-private partnerships for specific pilot solutions (e.g., mobile treatment) can be considered for rapid deployment. (Cape Town Government)
- Legal & regulatory levers: use environmental compliance notices, permit enforcement and, where warranted, administrative penalties to ensure polluters (including system operators) correct violations promptly. Transparent legal follow-through increases public confidence. (The Guardian)
- Community trust & communications: ongoing proactive communication is critical—share data in accessible formats, explain interventions and timelines, and provide channels for reporting new pollution events. Collaborate formally with citizen science groups to harness local capacity. (WaterCan)
- Performance metrics: define clear, measurable KPIs (e.g., rolling 30-day geometric mean of enterococci below threshold, number of emergency overflows per year, H₂S exceedance counts) that are published monthly. Independent verification should be budgeted. (Table Talk)
Milnerton Lagoon and Woodbridge Island face a multi-faceted pollution challenge dominated by sewage and compounded by stormwater, infrastructure constraints and legacy issues. While municipal initiatives (monitoring, pilot bioremediation and pledged upgrades) are underway, the persistence of odour events, independent test results and public concern show that action must be both faster and more transparent. A combination of immediate source-control, expanded monitoring, rapid repairs at the Potsdam WWTW and medium-term catchment interventions (stormwater control, sanitation upgrades and estuarine restoration) is necessary to protect public health, restore ecological function and secure the recreational and economic value of this coastal system. Stakeholder collaboration, independent oversight and open data are essential ingredients for success. (GroundUp News)
References(Note: key internet-sourced material used for this report is cited in-text with web.run reference tokens.)
GroundUp. (2024, December 13). Sewage stench lingers at Milnerton Lagoon. GroundUp. (GroundUp News)
Mail & Guardian. (2024, December 16). Sewage stench lingers at Milnerton Lagoon. Mail & Guardian (The Green Guardian). (The Mail & Guardian)
City of Cape Town. (2024). Interventions on track to improve Milnerton Lagoon’s water quality. City of Cape Town — Media and News. (Cape Town Government)
The Guardian. (2025, April 17). Kicking up a stink: row over sewage pollution blighting Cape Town's beaches. The Guardian. (The Guardian)
Table Talk. (2025, July 14). Milnerton Lagoon gets air monitoring boost. Table Talk. (Table Talk)
Rethink the Stink / WaterCAN / community sources. (2023–2025). Community testing and advocacy reports (citizen science results and campaign materials). (WaterCan)
Vernon Chalmers Photography. (2025, August). Water Quality Updates Milnerton Lagoon, Woodbridge Island. VernonChalmers.photography. (Local photographic documentation and commentary). (Vernon Chalmers Photography)
GroundUp. (2019). Polluted Milnerton lagoon "particularly disgusting". GroundUp (historical context).
Disclaimer
The 'Milnerton Lagoon / Woodbridge Island Pollution Status Report September 2025' was compiled by ChatGPT on the request of Vernon Chalmers Photography. Vernon Chalmers Photography was not instructed by any person, public / private organisation or 3rd party to request compilation and / or publication of the report on the Vernon Chalmers Photography website.
This independent status report is based on information available at the time of its preparation and is provided for informational purposes only. While every effort has been made to ensure accuracy and completeness, errors and omissions may occur. The compiler of this Pollution Report (ChatGPT 2025) and / or Vernon Chalmers Photography (in the capacity as report requester) disclaim any liability for any inaccuracies, errors, or omissions and will not be held responsible for any decisions made based on this information.
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