Introduction
How beaches can threaten public health
Major bacterial contaminants
Fecal indicator bacteria (FIB)
Pathogenic bacteria of concern
Sources and contributing factors
Methods of detection and monitoring
Strategies for staying safe
Policy, prevention, and research directions
Research gaps
Conclusion
References
Further reading
As beaches increasingly grapple with invisible microbial threats, cutting-edge detection, smarter policy, and informed choices are redefining what it means to swim safely.
Image Credit: Morocko / Shutterstock.com
Introduction
Human activity and climate change continue to threaten recreational water bodies with microbial contamination and pollution. This article examines current scientific insights into contamination sources, public health implications, and advanced technologies that are being implemented to modernize environmental monitoring. Practical recommendations are also provided to reduce exposure risks and inform safer public health policy.
How beaches can threaten public health
Recreational water environments, including coastal, estuarine, and freshwater bodies, offer numerous benefits for human health and well-being, while also promoting tourism and supporting local economies.1 Nevertheless, recreational water is associated with inherent risks due to potential exposure to pathogens, toxins, and irritants.2
Epidemiological studies have consistently reported an increased risk of illness, primarily those affecting the gastrointestinal (GI) tract, in individuals engaging in recreational water activities.2 Recreational water sources are also associated with several respiratory, eye, ear, nose, and throat (ENT) infections and various skin problems.2
GI symptoms are most frequently reported following exposure to contaminated recreational water. Importantly, waterborne infections have the potential to cause lethal effects, particularly in children, older adults, and immunocompromised individuals.2
Over half of U.S. beaches are potentially unsafe due to poop contamination | NBC New York
Major bacterial contaminants
Fecal indicator bacteria (FIB)
FIB are relatively harmless species of intestinally derived bacteria used as proxies for fecal water contamination and predictors of co-occurring harmful pathogens.3 Enterococcus spp. and Escherichia coli are the most common FIBs used to monitor microbial water quality.1,3
The EPA uses these bioindicators to establish robust Recreational Water Quality Criteria (RWQC, 2012), which specify statistical threshold values (STV), estimated illness rates (NGI), and geometric means (GM) for classifying contamination levels.3 For example, water bodies that exceed the NGI threshold of 32 and 33 Enterococcus and E. coli, respectively, can be restricted from public use until quality criteria are met.3
Pathogenic bacteria of concern
Most pathogenic bacteria in recreational bodies originate from fecal contamination, particularly human defecation.
Vibrio spp. are ubiquitous in marine and freshwater microbial communities globally. Although most species are harmless or minimally irritating, some, like Vibrio vulnificus and V. parahaemolyticus, can cause potentially life-threatening complications. These bacteria are often transmitted through the consumption of contaminated seafood or the exposure of open wounds to infected water.6
V. parahaemolyticus is the leading global cause of vibriosis. Comparatively, V. vulnificus is responsible for gastroenteritis, necrotizing fasciitis, and septic shock, with mortality rates exceeding 50% in high-risk individuals.6 V. vulnificus thrives in warm, brackish waters exceeding 18 °C, with climatic predictions suggesting its rise in response to global warming.6
Shigella, Salmonella, and Campylobacter infections can lead to bacillary dysentery, gastroenteritis, and profuse, watery diarrhea, respectively.7 These intestine-disrupting bacteria often enter recreational water through sewage or runoff.
Antibiotic-resistant bacteria (ARB) carry genes that confer resistance to commonly used antibiotics, which reduces or completely eliminates the effectiveness of standard pharmacological treatments during an infection. Previous studies suggest that recreational waters may be natural reservoirs for ARBs and antimicrobial resistance genes (ARGs), as these environments are conducive to their proliferation.8
Sources and contributing factors
Recreational water contaminants are generally categorized into ‘point sources’ that can be traced to a single, identifiable source like a pipe or a drain. Compared to contaminants from ‘point sources,’ those from ‘nonpoint sources’ are more diffuse and harder to address.9
Rainfall runoff, particularly from agricultural areas, and stormwater are the most significant contributors to water contamination. Both rainfall runoff and stormwater will concentrate pollutants and increase bacteria levels, in addition to transporting human and animal feces, as well as other chemical contaminants, to distant areas.9 Combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs) are also notable contributors, as these sewage overflows release billions of gallons of untreated sewage into waterways annually.9
Increased bather density has also been linked to a higher incidence of community-wide gastrointestinal and respiratory illnesses. Even 15 minutes of bathing time can contribute up to six million colony-forming units (CFU) of Staphylococcus aureus.1,2
The environment has also been implicated in water contamination, as rainfall and tidal movements can influence the concentration and dissemination of microorganisms. Temperature affects the growth and survivability of pathogens like V. vulnificus, as observed in the spike of cyanobacterial harmful algal blooms (CyanoHABs) in response to global warming.1,6 ,9
Methods of detection and monitoring
Since the development of fecal indicator-leveraging most probable number (MPN) procedures in the 1950s, numerous methods have been rigorously standardized. For example, the 2012 Recreational Water Quality Criteria (RWQC) provides updated guidelines on FIB procedures to ensure timely monitoring of water quality and urgent intervention when indicated.1,3
Recent genetic technologies, such as rapid quantitative polymerase chain reaction (qPCR), have expedited biological contamination monitoring by reducing identification times from the two to four days required for traditional culture methods to just a few hours.9 Metagenomics, a next-generation DNA-based approach, has also emerged as a novel method for providing rapid and non-targeted assessments of biological contaminants.
Hyperspectral remote sensing is another indispensable tool for water monitoring, available through various platforms, including moorings, unmanned aerial vehicles (UAVs), airborne systems, and spaceborne satellites. Biosensors that leverage biological analytes to monitor water quality in real-time are also being increasingly deployed and refined.
Despite the potential utility of recent innovations, these technologies are often expensive and require extensive technical expertise. Taken together, these limitations limit their potential for widespread application, particularly in underprivileged and marginalized regions.1,9
Strategies for staying safe
Improving public health authority-mediated infrastructure, public education, and advanced monitoring systems is essential for ensuring public safety in recreational bodies of water. User responsibility is also important, with beachgoers advised to maintain optimal hygiene practices such as showering before swimming, actively avoiding swallowing water, and refraining from activities if they are sick or have open wounds.1
Understanding water quality signs is crucial, as this knowledge enables real-time decisions about exposure risk. When in doubt, beachgoers should consult the local beach authority's website for advisories and current conditions.1
Image Credit: Mr.Emre.B / Shutterstock.com
Policy, prevention, and research directions
The United States Environmental Protection Agency (EPA) and the World Health Organization (WHO) cite scientific reports to emphasize that recreational waters are vulnerable to contamination from diverse sources, including stormwater, urban and agricultural runoff, industrial discharge, sewage treatment systems, and atmospheric deposition.1,3
The EPA and WHO also actively establish guidelines on water quality monitoring methodologies, recommend safety criteria, and support risk management efforts. Simultaneously, research aims to improve current pollutant monitoring, risk assessment, and impact mitigation infrastructure.1,3-5
Modernizing wastewater systems and upgrading treatment protocols are crucial for mitigating sources of recreational water pollution.9 Green Stormwater Infrastructure (GSI) solutions, such as bioswales, rain gardens, and green roofs, offer nature-based alternatives that effectively slow, absorb, and filter stormwater at its source.1
Effective surveillance and water quality monitoring systems are indispensable for timely information on water quality alerts and confirmed discharges, thereby empowering beachgoers to make informed decisions.1 Community science programs can complement official monitoring by providing cost-effective, participatory approaches to environmental monitoring and policy implementation.10
Research gaps
Microbial Source Tracking (MST) is a valuable tool for distinguishing human fecal contamination from that of animal origin. Despite its utility, additional research is needed to determine whether the specific source modifies indicator-health associations.3,4
Reliable national-level indicators for health effects directly associated with contaminated beach waters are often unavailable, especially in developing and underdeveloped regions. This may be due to under-reporting of common ailments and the inherent difficulties associated with directly connecting these symptoms to water exposure. Thus, ongoing and robust surveillance is crucial for verifying health impacts and generating evidence to meet national health-based targets.1,3
Conclusions
Bacterial contamination of recreational waters is a persistent and growing public health concern that is exacerbated by climate change, outdated infrastructure, and inadequate monitoring. Although scientific advances, such as qPCR and metagenomics, offer faster and more reliable detection, their equitable implementation remains challenging.
Swimmers and policymakers can actively reduce exposure risks by adopting better hygiene practices, enhancing infrastructure, and making data-informed decisions. Empowering local communities and addressing research gaps in source tracking, surveillance, and method standardization will further preserve recreational waters for future generations.
References
- World Health Organization. (2021). Guidelines on Recreational Water Quality: Volume 1 Coastal and Fresh Waters. World Health Organization. https://www.ncbi.nlm.nih.gov/books/NBK572632/ Accessed 10 July 2025.
- Russo, G. S., Eftim, S. E., Goldstone, A. E., Dufour, A. P., Nappier, S. P., & Wade, T. J. (2020). Evaluating health risks associated with exposure to ambient surface waters during recreational activities: A systematic review and meta-analysis. Water Research, 176, 115729. DOI – 10.1016/j.watres.2020.115729. https://pubmed.ncbi.nlm.nih.gov/32240845/
- US Environmental Protection Agency. (2017). 2017 Five-Year Review of the 2012 Recreational Water Quality Criteria. United States Environmental Protection Agency. https://www.epa.gov/sites/default/files/2018-05/documents/2017-5year-review-rwqc.pdf. Accessed 10 July 2025.
- Hong, P.-Y., Mantilla-Calderon, D., & Wang, C. (2020). Metagenomics as a Tool To Monitor Reclaimed-Water Quality. Applied and Environmental Microbiology, 86(16). DOI – 10.1128/aem.00724-20. https://www.researchgate.net/publication/341942640_Mini_Review_Metagenomics_as_a_tool_to_monitor_reclaimed_water_quality
- Moses, W. J., Vander Woude, A. J., & Palacios, S. L. (2022). Emerging technologies and techniques for remote sensing of coastal and inland waters. Frontiers in Environmental Science, 10. DOI – 10.3389/fenvs.2022.1028307. https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2022.1028307/full
- Candelli, M., Sacco Fernandez, M., Triunfo, C., Piccioni, A., Ojetti, V., Franceschi, F., & Pignataro, G. (2025). Vibrio vulnificus—A Review with a Special Focus on Sepsis. Microorganisms, 13(1), 128. DOI – 10.3390/microorganisms13010128. https://www.mdpi.com/2076-2607/13/1/128
- Public Health Agency of Canada. (2024). Guidelines for Canadian Recreational Water Quality Guideline Technical Document – Microbiological Pathogens and Biological Hazards. Government of Canada. https://www.canada.ca/en/services/health/publications/healthy-living/guidelines-canadian-recreational-water-quality-guideline-technical-document-microbiological-pathogens-biological-hazards.html. Accessed 10 July 2025.
- Nappier, S. P., Liguori, K., Ichida, A. M., Stewart, J. R., & Jones, K. R. (2020). Antibiotic Resistance in Recreational Waters: State of the Science. International Journal of Environmental Research and Public Health, 17(21), 8034. DOI – 10.3390/ijerph17218034. https://pmc.ncbi.nlm.nih.gov/articles/PMC7663426/
- Olds, H. T., Corsi, S. R., Dila, D. K., Halmo, K. M., Bootsma, M. J., & McLellan, S. L. (2018). High levels of sewage contamination released from urban areas after storm events: A quantitative survey with sewage-specific bacterial indicators. PLOS Medicine, 15(7), e1002614. DOI – 10.1371/journal.pmed.1002614. https://pmc.ncbi.nlm.nih.gov/articles/PMC6057621/
- Welch, C. P., Rudko, S. P., Peter, B., Klimchuk, S., Gill, K., Lu, R. X., & Hanington, P. C. (2025). From bench to beach: Assessing the reliability of community-based qPCR monitoring for recreational water quality. PLOS Water, 4(5), e0000309. DOI – 10.1371/journal.pwat.0000309. https://journals.plos.org/water/article?id=10.1371/journal.pwat.0000309
Further Reading