Recent research has raised concerns that current water-quality testing methods may not adequately protect public health at popular bathing sites. Studies indicate that swimmers are experiencing gastrointestinal and other illnesses even when standard tests for faecal bacteria suggest water is safe.

Researchers from Griffith University in Australia analyzed nine studies—eight at coastal locations and one at a freshwater site—finding that swimmers were more likely than non-swimmers to report diarrhoea, vomiting, and irritation of the ears, eyes, skin, or respiratory system. These illnesses occurred despite water samples meeting established safety thresholds for bacteria commonly used as indicators, such as E.coli and intestinal enterococci.

Traditionally, water safety has been assessed by measuring the concentration of these bacteria, which indicate recent faecal contamination. Current guidelines in many countries, including England, require that E.coli levels remain below 250 per 100 millilitres for an “excellent” rating at coastal sites, with slightly higher allowable limits for inland waters. However, experts caution that these bacteria may not correlate well with the presence of viruses or other pathogens that cause illness.

Anne Leonard, a water quality specialist, notes that while E.coli and enterococci serve as useful markers for bacterial contamination, they do not reliably indicate the presence of viral pathogens such as norovirus and rotavirus, which are known to persist through wastewater treatment and pose significant health risks to swimmers.

The World Health Organization (WHO) and the UK Environment Agency maintain that testing for every possible pathogen in recreational waters would be costly and time-consuming, so testing focuses on faecal indicators as a proxy. However, some scientists challenge this approach. A 2023 review published in the Journal of Water and Health suggested that relying solely on bacterial markers can both underestimate and overestimate the risk posed by human enteric viruses.

Recent outbreaks have underscored these concerns. In 2024, over 180 people reported illness after swimming at a lake in Cardiff, with most cases linked to norovirus infection. Additionally, in 2025, the UK Health Security Agency recorded 115 cases of leptospirosis—a serious bacterial disease transmitted through water contaminated with animal urine. One severe case involved a 68-year-old man from Derby who became critically ill after exposure to contaminated water.

Some experts advocate expanding testing protocols to include other indicators. Professor Sunny Jiang of the University of California suggests monitoring coliphages—viruses that infect bacteria—as these may better signal faecal contamination. A study last month from the University of East Anglia found that in Hungarian rivers and lakes meeting EU standards, combining coliphage measurements with E.coli levels more accurately predicted swimmer illness than intestinal enterococci alone.

Experts also highlight that measurement frequency and sampling locations may limit the effectiveness of current monitoring. The Environment Agency collects between five and 20 samples per site across the bathing season, which may not capture rapid changes in water quality caused by heavy rains or sewage overflows. A 2024 warning from the Office for Environmental Protection stressed that testing at a single point can miss pollution elsewhere along a site.

Local environmental concerns have been raised at sites such as Avon Beach near Christchurch Harbour, where untreated sewage discharged into the River Stour contributes to elevated bacterial levels. In August 2024, bacterial counts reached 370,000 E.coli per 100 millilitres in the river, leading to event cancellations and illness among visitors, including a severe antibiotic-resistant infection in a young child.

Authorities emphasize ongoing monitoring efforts. An Environment Agency spokesperson stated that water quality at 464 designated bathing sites is regularly checked during the season, and the public is encouraged to consult official sources for current safety information. Bournemouth, Christchurch and Poole Council acknowledged that while individual infection cases are difficult to trace, there have been no official alerts suggesting a widespread outbreak.

As evidence mounts that traditional faecal indicator bacteria may not fully capture microbial risks, some scientists, including those involved in developing international guidelines, call for broader surveillance of emerging pathogens, microbial toxins, and antibiotic-resistant organisms to better protect public health at recreational waters.