Coastal wastewater pollution is measured through several connected signals: sewage reaching marine waters, beach advisories, nutrient impairment, oxygen stress, and the cost of repairing treatment and conveyance systems. The available assessments span a 2018 global review, 2010s Caribbean estimates, the 2023 U.S. swimming season, and older U.S. wastewater estimates, so each figure below retains its original period and geography.
Contents
- Global and regional scale
- Beach advisories and swimming disruption
- Reported pollution sources at U.S. beaches
- Sewer overflows and untreated discharges
- Nutrients and coastal oxygen stress
- Infrastructure needs
- Coastal case studies
Global and regional scale
The United Nations Environment Programme’s Wastewater Pollution on Coral Reefs brief reported in its 2018 assessment that more than 80% of marine pollution originates from land-based wastewater, sediment, and nutrients delivered through waterways. That figure describes a broad group of land-based pressures rather than wastewater alone, but it places coastal pollution in a watershed context: what enters rivers and drainage systems can ultimately affect reefs, estuaries, and shorelines.
The same 2018 assessment estimated that major rivers in Southeast Asia discharge about 600,000 tonnes of nitrogen into the ocean each year. It also forecast that global nitrogen inputs to the ocean would increase by at least 14% by 2030. The forecast is not a measurement of 2030 conditions; it is a projected change from the assessment’s baseline.
Caribbean estimates show the treatment gap more directly. UNEP’s Protocol Concerning Pollution from Land-Based Sources and Activities estimated that more than 75% of sewage entering the Caribbean Sea was untreated or only partially treated during the 2010s regional estimate period. The protocol also estimated annual land-based inputs of 13,000 tonnes of nitrogen and 5,800 tonnes of phosphorus to the Caribbean Sea.
These figures measure different things. The global and Southeast Asian numbers describe marine inputs or projected change, while the Caribbean figures describe sewage treatment and estimated nutrient loads. Together, they show why coastal wastewater pollution is not represented by beach closures alone: the same watershed can transmit pathogens, organic matter, nitrogen, and phosphorus across different distances and timescales.
Beach advisories and swimming disruption
The U.S. Environmental Protection Agency’s Beach Report: 2023 Swimming Season recorded 697,737 available beach days at participating coastal and Great Lakes program beaches. Beaches were open and without advisories 91% of the time. Advisories or closings were reported on 62,131 beach days.
At the beach level, 1,541 of 5,090 program beaches—30%—had at least one advisory or closing during the 2023 swimming season. States, territories, and Tribes issued 8,088 coastal beach advisories or closings. These are notification actions, not a count of unique pollution events, because one event can produce a notification and a single beach can receive more than one notification.
The duration data gives additional context. Seventy-seven percent of 2023 beach notification actions ended within a week after bacteria levels fell below applicable thresholds. Seventeen percent lasted only one day, while 16% ended between one and two days. Short notifications can still disrupt swimming, but the duration distribution distinguishes brief responses from longer closures.
The national program statistics also have a defined scope. They cover participating U.S. coastal and Great Lakes beaches, not every shoreline or every day at every U.S. beach. The results are therefore best read as a monitoring-program picture of public swimming disruption during the 2023 season.
Reported pollution sources at U.S. beaches
EPA’s 2023 beach report associated reported pollution sources with both wastewater systems and non-wastewater pathways. The source counts below are reported source associations, and their displayed percentages refer to the report’s source total.
| Reported source | Sources | Share of reported total |
|---|---|---|
| Stormwater runoff | 1,207 | About 20% |
| Wildlife | 427 | About 7% |
| Dry-weather runoff | 264 | About 4% |
| Boat discharge | 199 | About 3% |
| Sewer-line leakage | 142 | About 2% |
| Sanitary sewer overflows | 139 | About 2% |
| Septic-system leakage | 120 | About 2% |
| Publicly owned treatment works | 87 | About 1% |
| Combined sewer overflows | 84 | About 1% |
The report also associated agricultural runoff with 61 sources, or about 1% of the reported total. Concentrated animal feeding operations accounted for 27 sources, under 1%; harmful algae accounted for 17 sources, also under 1%.
The wastewater-related categories should not be added to create a single wastewater total without a defined classification method. A treatment plant, a sewer overflow, a leaking sewer line, and a leaking septic system represent different failure points. Stormwater runoff can also carry sewage-related contamination, nutrients, and other pollutants, but the report lists it as its own reported source category.
Sewer overflows and untreated discharges
Older EPA estimates illustrate the scale of U.S. sewer-system exposure, while retaining their 2004 measurement period. EPA estimated that 772 combined sewer systems in 31 states and the District of Columbia discharged 850 billion gallons of untreated wastewater and stormwater annually. The agency’s estimate covered about 19,000 municipal sanitary sewer collection systems serving about 160 million people, roughly 58% of the U.S. population at that time.
For sanitary sewer overflows, EPA estimated 23,000 to 75,000 events per year and 3 to 10 billion gallons of wastewater discharged per year. The wide ranges signal estimation uncertainty and variation in system conditions; they should not be interpreted as a single precise annual count.
The same 2004 EPA summary reported that municipal treatment facilities collected and discharged more than 11 trillion gallons of treated wastewater annually. Treated wastewater and untreated overflow are different discharge categories, so the treated volume is not an estimate of pollution released without treatment.
EPA estimated 3,500 to 5,500 gastrointestinal illnesses per year from combined sewer overflows and sanitary sewer overflows at regularly monitored coastal and Great Lakes beaches. This is a 2004 estimate tied to the agency’s stated beach and overflow context, not a current national illness count.
The infrastructure estimates reported in the same source were substantial. A 2000 needs estimate, reported by EPA in 2004, put the cost of reducing combined sewer overflow volume by 85% at about $50.6 billion over 20 years. Controlling sanitary sewer overflows was estimated at about $88.8 billion over 20 years. By 2004, seven major municipal enforcement cases had eliminated approximately 14 billion gallons of sewage overflows per year.
Nutrients and coastal oxygen stress
Wastewater pollution can affect coastal ecosystems through nutrients as well as pathogens. EPA’s cited 2009 assessment found impairment from nutrient pollution in about two-thirds of U.S. coastal areas. More than one-third of U.S. estuaries showed nutrient impairment in that assessment.
Nutrient impairment can be associated with excessive plant and algae growth and subsequent oxygen stress, but the supplied figures do not quantify a single nationwide area of hypoxia or attribute every impaired water body to wastewater. The measured claims are the percentages of coastal areas and estuaries identified as impaired by nutrient pollution in the cited 2009 assessment.
The Long Island Sound Study provides a dated reduction target. Its 1998 target called for a 58.5% reduction in human-source nitrogen loads from 1990 levels by 2014. By 2009, New York and Connecticut were approximately 55% of the way toward that nitrogen-reduction goal. “Approximately 55% of the way” describes progress toward the stated target; it does not mean a 55% reduction from the 1990 baseline.
Infrastructure needs
EPA’s 2022 Clean Watersheds Needs Survey reported $630.1 billion in total U.S. clean-water infrastructure needs. The survey covered 17,544 reported publicly owned treatment works serving 270.4 million people.
The wastewater and stormwater categories show how pollution control depends on more than treatment-plant upgrades:
- Secondary wastewater treatment: $66.6 billion.
- Advanced wastewater treatment: $83.6 billion.
- Conveyance-system repair and new conveyance systems: $151.1 billion.
- Combined sewer overflow correction: $36.5 billion.
- Stormwater management: $115.3 billion.
- Decentralized wastewater treatment systems: $74.7 billion.
These are reported needs from the 2022 survey, not completed spending and not a forecast of actual project costs. Conveyance, stormwater, combined sewer, and decentralized-system needs are especially relevant to coastal pollution because contamination can reach receiving waters before treatment is completed or where runoff and wastewater pathways intersect.
Coastal case studies
EPA’s Beach Impact Comparison Study modeled wet-season Tijuana River transboundary flows and found that the Tijuana River caused 66.7% of modeled regional beach closures, while SAB Creek caused 33.3%. The result applies to the study’s 2017 modeled flows, not to all years or all regional closures.
The same study associated SAB Creek wastewater flows with 109 dry-season days of modeled regional beach-closure impact. This example links a wastewater flow pathway with a modeled beach-closure consequence, while preserving the distinction between modeled impact days and an observed count of all beach closures.
The Charles River case study shows a large reduction associated with infrastructure work. EPA reported that combined sewer overflows to the Charles River fell from 1.7 billion gallons per year in 1988 to 6.88 million gallons per year after the infrastructure work. EPA described the wastewater-control program as a $1 billion investment in its 2006 case-study report.
The Charles River figures are a before-and-after case study with an explicitly stated 1988 baseline and post-project result. They do not establish that the same reduction occurred across U.S. sewer systems, but they demonstrate how investment in overflow control can be reflected in a measured discharge-volume change.