Why the Study Was Conducted
What Wastewater Does to Marine Ecosystems
Does This Invalidate Marine Protection?
Technologies Available to Address the Problem
What Must Be Done
References and Further Reading
A recent study published in Ocean & Coastal Management has confirmed what many coastal ecologists have long suspected but lacked the data to quantify: marine protected areas (MPAs) are failing to keep out one of the ocean's most pervasive threats.
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The study found that 73 % of the world's 16,491 MPAs are contaminated by sewage-derived wastewater.1 In tropical regions, the problem is considerably worse. Between 87 % and 92 % of protected areas in coral reef zones are affected, with nitrogen concentrations from sewage running 10 times higher inside these zones than in adjacent unprotected waters.1
Why the Study Was Conducted
The impetus for the research was practical: the global community is racing toward the "30 by 30" target under the Kunming-Montreal Global Biodiversity Framework - a commitment to place 30 % of the world's ocean under protection by 2030.
Lead author David E. Carrasco Rivera and co-author Dr. Amelia Wenger of WCS used geospatial modeling to map wastewater nitrogen flow from land-based sewage systems across all major MPA boundaries, comparing pollution exposure inside protected zones against nearby unprotected waters.1
The motivation was to test a fundamental assumption: that designating an area as protected translates into meaningful ecological protection. The answer, at least with respect to land-based pollution, is largely no. A perfectly managed MPA cannot prevent pollution that originates upstream on land from flowing in. No physical or regulatory barrier inside a marine zone can stop a river or stormwater drain.1
The six tropical sub-regions examined, Australasia and Melanesia, Mesoamerica and the Caribbean, the Coral Triangle, East Africa, the Indian Ocean, and the Middle East and North Africa, were specifically chosen because they contain the highest concentrations of biodiversity-rich and economically critical marine habitats.1 These are precisely the places where failure is most consequential.
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What Wastewater Does to Marine Ecosystems
Wastewater is not a single contaminant. It is a compound mixture of nutrients, pathogens, heavy metals, pharmaceuticals, endocrine disruptors, and microplastics. When this load reaches coastal waters, it drives eutrophication - excess nutrient inputs that fuel algal blooms, reduce light penetration, and deplete dissolved oxygen. Coral reefs, which depend on nutrient-poor, clear water, are highly vulnerable. Seagrass meadows, already under pressure from sediment and warming, are smothered by epiphytic algal overgrowth stimulated by elevated nitrogen.2
A 2025 study published in Environmental Pollution reinforced these findings, tracking pollution levels over a decade across oceanic MPAs in the South Atlantic and concluding that sewage contamination had increased substantially within those protected zones over 10 years. Its central finding was unambiguous: without pollution control, MPAs fail to protect reefs even in remote oceanic settings.3
Previous research has also linked coastal wastewater exposure to coral disease, harmful algal blooms, and, more recently, neurological disease analogous to Alzheimer's in dolphins.1 The consequences for human populations are equally serious. Contaminated coastal waters are estimated to cause up to 1.4 million deaths annually from waterborne diseases, including cholera and typhoid, and generate up to $12 billion in economic losses globally.1
Does This Invalidate Marine Protection?
The study does not argue that MPAs are without value - far from it. What it demonstrates is that area-based protection, when measured against a checklist of targets, can produce an illusion of progress if water quality is not addressed alongside habitat designation.
Under the Global Biodiversity Framework, Target 3, the 30x30 area protection goal, is explicitly linked to Target 1 (land and sea use planning), Target 2 (restoration), and Target 7 (pollution reduction).1 The study's warning is that governments pursuing acreage metrics alone are building protected zones that cannot deliver on the ecological outcomes those designations were designed to secure.4
A World Bank report places the global water-sector spending shortfall above $131 billion per year, meaning the infrastructure investment needed to close this gap is substantial but not incalculable. The study argues that conservation funding should be redirected upstream to wastewater infrastructure as a prerequisite for effective ocean protection.
Technologies Available to Address the Problem
Solutions exist across a spectrum of technical complexity and cost, and several are already being deployed in coastal regions.
Advanced wastewater treatment plants remain the most direct intervention. Research published in Marine Pollution Bulletin in 2025 examined multiple treatment processes and found that the Modified A²/O+AO process showed the highest comprehensive performance across indicators, including nitrogen removal, BOD removal, and phosphorous reduction.5 For countries with existing infrastructure, upgrading treatment capacity specifically to remove nutrients before discharge is the most immediate option.
Membrane Bioreactor (MBR) systems represent a high-efficiency alternative for coastal and maritime settings. During the 2024 Alaska cruise season, 14 vessels equipped with Wärtsilä's Hamworthy MBR systems achieved a 98.2 % regulatory compliance rate under independent environmental testing, illustrating their effectiveness in high-volume, space-constrained applications.6 Scaled for coastal municipalities adjacent to MPAs, this technology could substantially reduce nutrient loads entering protected zones.
Constructed wetlands (CWs) offer a lower-cost, nature-based treatment pathway particularly relevant for lower-income tropical regions - exactly those identified as most at risk. A 2024 synthesis of data from 364 CW sites worldwide found removal efficiencies for organic matter and nutrient pollutants in the range of 68–84 % at the 75th percentile, with synergistic pollutant removal effects that persisted for 3–12 years of operation.7
Capital, energy, and maintenance costs for constructed wetlands collectively amount to approximately 50 %, 28 %, and 20 %, respectively, of those associated with conventional treatment plants - a significant cost advantage for resource-limited governments.7 In the Dominican Republic, The Nature Conservancy has already partnered with local authorities to implement treatment wetlands at the watershed level with documented success in reducing pollution loads reaching coastal zones.2
Wastewater reuse legislation has also proven effective as a policy tool. Florida's 2008 Ocean Outfall Law, which mandated advanced treatment and required 60 % reuse of baseline wastewater flows while phasing out direct ocean discharge by 2025, has progressively reduced the volume of treated effluent entering coastal waters near sensitive reef systems. Between 2008 and 2018 alone, reclaimed water across its seven permit holders increased from 32 to 43.5 million gallons per day.8
IoT-enabled monitoring systems are increasingly being integrated into coastal water quality management. Real-time sensor networks capable of tracking nitrogen, pathogen indicators, and turbidity can give conservation managers early warning of pollution events and provide the data necessary to trigger enforcement action or redirect flows before damage occurs.5
What Must Be Done
The study's authors are explicit about the policy shift required: sewage management must be integrated into MPA design, siting, and effectiveness evaluation from the outset - not treated as a separate environmental issue managed by a different government department.1 Conservation planners need watershed-level water quality data before designating new MPAs, and existing MPAs require updated management plans that account for upstream land use.
Multilateral funding mechanism, including those attached to the Global Biodiversity Framework and international climate finance, should be directed toward upstream wastewater infrastructure as a recognized component of ocean conservation spending. The current separation of marine conservation budgets from water and sanitation budgets is itself part of the problem.
The 30x30 target is not wrong. It is necessary but insufficient. What this research makes clear is that protected status on paper, without parallel investment in the land-based systems that determine water quality, will not deliver the ecological outcomes the framework promises. The ocean's protected areas cannot protect themselves from what flows into them from shore.
References and Further Reading
- Carrasco Rivera, D. E., & Wenger, A. S. (2026). Wastewater pollution undermines coastal marine protection: Implications for 30x30 and effective conservation. Ocean & Coastal Management, 276, 108150. https://doi.org/10.1016/j.ocecoaman.2026.108150
- Zimmer-Faust, A. (2023). Wastewater pollution and the fight for coastal resilience. Cool Green Science; The Nature Conservancy. nature.org
- Mello, T. J., Longhini, C. M., Wanderley, B. M. S., da Silva, C. A., Lehrback, B. D., Bom, F. C., Rodrigues Neto, R., Sá, F., Vieira, E. A., Costa, V. E., & Longo, G. O. (2025). Pollution affects even oceanic marine protected areas in the Southwestern Atlantic. Environmental Pollution, 366, 125485. https://doi.org/10.1016/j.envpol.2024.125485
- Earth.com. (2026). Over 70% of protected ocean areas are polluted by sewage. Earth.com Science News. https://www.earth.com/news/over-70-of-protected-ocean-areas-are-polluted-by-sewage/
- Kurniawan, S. B., Roziqin, A., Ahmad, A., Ahmad, M. M., Alfanda, B. D., Pambudi, D. S. A., Said, N. S. M., Abdul, P. M., & Imron, M. F. (2026). Tackling marine pollution in the blue economy: Synergies between wastewater treatment technologies and governmental policies. Marine Pollution Bulletin, 222, 118627. https://doi.org/10.1016/j.marpolbul.2025.118627
- Alaska Department of Environmental Conservation. (2024). Commercial passenger vessel environmental compliance program: 2024 wastewater discharge data. State of Alaska DEC. https://dec.alaska.gov/water/cruise-ships/cruise-reports/
- Li, X., Wu, S., & Dong, R. (2024). Sustainability of global small-scale constructed wetlands for multiple pollutant control. npj Clean Water, 7(1), 12. https://doi.org/10.1038/s41545-024-00336-3
- Reef Resilience Network. (2024). Florida – Wastewater pollution and the Ocean Outfall Law case study. TNC Reef Resilience. https://reefresilience.org/case-studies/florida-wastewater-pollution/
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