By Amelia Wenger, Water Pollution Lead, Wildlife Conservation Society, and Jonathan Kelsey, Director, Bloomberg Ocean Fund

The sewage pollution crises unfolding across the world are impossible to ignore. A problem that has been bubbling under the surface for decades has broken into the mainstream, and the public are rightfully outraged.

In the US, more than 240 million gallons of untreated waste recently spilled into the Potomac River – a key drinking water source for millions – with long-term ecological impacts expected. Meanwhile, in England, raw sewage was discharged into rivers and seas nearly 300,000 times last year, contaminating waterways, closing beaches, and making swimmers sick.

This is a systemic public health and environmental crisis. But, until now, what has been far less understood is where this pollution is flowing. The answer, as it turns out, is into some of the ocean’s most important and protected areas.

A new global study by the Wildlife Conservation Society (WCS) and University of Queensland, Australia, uncovers a fundamental gap in how we are protecting and conserving the ocean. The study tracks sewage pollution across over 16,000 marine protected areas (MPAs) worldwide.

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Pollution is widespread, systemic – and, alarmingly, often worse inside MPAs

Nearly three-quarters (73%) of MPAs are polluted, and levels are often ten times higher than in surrounding waters. Many MPAs are located near coastlines, markets, and population centers, where fishing pressure is high but also where wastewater pollution is most likely to occur.

Yet in most cases, pollution is not factored into MPA design, even when listed as a threat in management plans. The design of MPAs is disconnected from one of the most serious pressures they face, compromising the biodiversity, economic and food security, and other benefits they are established to deliver. In short, we are protecting waters without addressing the pollution flowing into them.

The scale of the problem is substantial. The study finds that in some of the world’s most important coral reef regions, up to 92% of protected areas were impacted. Meanwhile, global estimates show that 55% of coral reefs and 88% of seagrass ecosystems are exposed to wastewater pollution, which leaves them less resilient to the climate crisis.

Exposure to pollution has drastic consequences. Nutrients, pathogens, and chemicals found in wastewater are toxic, driving ecosystem decline and damaging marine health. Scientists have even linked wastewater to an Alzheimer’s-like brain disease in dolphins. Algae blooms can devastate coral reefs – an essential ecosystem, home to one quarter of marine life and worth around GBP 300 billion every year.

Pollution also poses a direct threat to people. Swimmers become sick after entering waters contaminated with sewage, chemicals, and waste. Beaches that should be places of recreation and well-being are becoming health hazards, exposing people to infections and, in some cases, leading to hospitalization.

The impacts extend far beyond public health. Pollution can devastate the tourism economies many coastal communities depend on, while also contaminating fish and other marine resources that support food security and livelihoods.

Tackling wastewater pollution is therefore essential, both for human well-being and to safeguard the ocean.

MPAs work – but they can’t succeed in isolation

When effectively designed and managed, the potential benefits of MPAs are huge. They are one of the most effective tools we have to restore the ocean, rebuild fish stocks, and, in turn, support food security and a broad range of livelihoods.

In fact, achieving the Kunming-Montreal Global Biodiversity Framework’s (GBF) 30×30 target – truly protecting and conserving at least 30% of the ocean by 2030 – could unlock USD 85 billion in annual returns and avoided costs by 2050. These returns are from three key benefits alone: preserving natural coastal defenses, avoiding carbon emissions from seagrass loss, and restoring overexploited fisheries.

But MPAs cannot prevent pollution from flowing into them. While they are vital for safeguarding ecosystems from destructive activities, their effectiveness is limited when pollution threats go unmitigated. This disconnect risks weakening the impact of 30×30.

The global response to marine conservation highlights this imbalance. International momentum and political ambition have coalesced around the 30×30 target, driving coordinated action to establish and expand MPAs worldwide. By contrast, there is no comparable global agreement, initiative, or sustained political focus on addressing sewage and wastewater pollution, despite its escalating impacts on marine ecosystems. At the same time, scientific attention to water pollution has steadily declined, with records of pollution management falling since the 1970s-1990s, despite the scale of the problem intensifying globally.

Without understanding and addressing pollution at the source, even well-designed MPAs will struggle to deliver meaningful ecological and economic outcomes.

Addressing pollution to achieve 30×30

If 30×30 is to deliver effective and equitable ocean protection, our approach must change.

We must move away from a model that siloes ocean protection toward one that connects land and sea. This means integrating management of impacts flowing from land with those happening in the ocean, embedding wastewater pollution reduction into conservation strategies, and strengthening coordination across government. Simultaneously, we must direct investment in the blue economy towards improving sanitation infrastructure and reducing pollution at the source.

The challenge is clear, but so is the path forward. As governments and funders move from ambition to delivery, they must ensure that actions to expand ocean protection are matched by investments to reduce the external pressures that undermine it. We must use the full set of tools available, from MPAs to wastewater management, to address the pressures facing marine ecosystems.

30×30 is a critical goal – one of many interconnected targets needed to truly restore ocean health. Ultimately, it will be judged not just by how much of the ocean is designated as protected, but by how effectively those areas are safeguarded.