TMU study: Seagulls a key contributor to health risks when water contamination rises at beaches in Canada

TORONTO — A new study led by Toronto Metropolitan University (TMU) has found that the water quality at publicly monitored beaches in Canada is generally safe for swimming, while also showing that seagull contamination is a previously under-recognized contributor to health risks.

Led by professor Ian Young, the study was conducted between 2023-25 at popular beaches in Ontario (Toronto and Niagara regions), Vancouver, Manitoba and Halifax.

QUICK FACTS

• Study found Canadian beaches generally safe for swimming
• Rates of reported gastrointestinal illness were low among beach-goers
• During an occasional spike in water contamination, seagulls play a consistent role in elevated E. coli levels, which are associated with higher risk of gastrointestinal illness—especially when swimmers swallow water, the study found

Researchers monitored the Canadian beaches to understand how water quality translates into real-world health risks for swimmers.

Across all sites, researchers found that overall rates of reported gastrointestinal illness—including symptoms such as vomiting and diarrhea—were low after going to the beach, affecting approximately 2.6 per cent of participants.

The study found that among those participants, illness risk increased among those who swam in the water, particularly those who reported swallowing water. Higher levels of E. coli—an indicator of fecal pollution—in the water were also associated with increased risk of illness.

Importantly, the study used advanced DNA “source tracking” techniques to identify where contamination was coming from. While markers of human sewage were detected at low levels at some sites, researchers found that when water had higher levels of E. coli, this was mostly due to higher levels of seagull-related contamination.

Seagull contamination was also associated with increased gastrointestinal illness risk—an emerging finding that has not been widely reported in previous beach water quality research, which has typically focused on human sewage sources.

“We found that while beaches are generally quite clean and safe, there are still occasional spikes in contamination,” said TMU professor Ian Young.

“What stood out in this study was the consistent role of seagulls, and the fact that higher levels of E. coli—often linked to seagull activity—were associated with increased risk of illness, especially when people swallowed water," he said.

The study also reinforces the relevance of existing public health guidelines for recreational water use. Researchers found that current thresholds used by health authorities to issue swimming advisories appear to be effective indicators of increased risk.

“When those guideline levels were exceeded, we did see higher risk,” Young added. “Overall, the guidelines are a useful and protective tool for the public to make informed decisions about when to swim at public beaches.”

The study suggests that environmental factors such as wildlife activity can temporarily influence water quality.

The findings are based on field research involving beach water sampling and surveys of swimmers’ activities and health outcomes following beach visits.

Interview Opportunity:
To request an interview with professor Ian Young, please contact Lindsey Craig at lindseyc@torontomu.ca

Media contact:
Lindsey Craig
PR & Communications Specialist
Toronto Metropolitan University
lindseyc@torontomu.ca