A recent study by researchers at the University of East Anglia in the United Kingdom has raised concerns about the health risks of swimming in freshwater environments, even in areas that meet European Union water quality standards. The study, published in the International Journal of Hygiene and Environmental Health, involved 2,368 people who swam in lakes and rivers in Hungary. Participants had to swim for about ten minutes and submerge their heads under water three times. The findings showed that 2.1% of swimmers developed gastroenteritis — a stomach illness that causes diarrhea and vomiting — compared to 1.9% of people who stayed on the shore. Additionally, 2.7% of swimmers experienced skin issues like redness, itching, and ulcers, compared to just 1.3% of non-swimmers. The study identified several biological contaminants in the water, including high levels of bacteria such as Escherichia coli (E. coli) and enterococci, which are often linked to fecal pollution and can cause gastrointestinal illnesses. Researchers also suspect that cercaria, a parasitic larva that can penetrate human skin, may be responsible for some of the skin problems observed. The risk of gastroenteritis, the study found, increased with higher concentrations of E. coli and viruses that infect human intestinal bacteria — both of which are indicators of fecal contamination in water. While the study did not examine cyanobacteria, these organisms — also known as blue-green algae — can thrive in warm, stagnant water during the summer. When they multiply rapidly, they can release toxins that may cause headaches, liver damage, or neurological problems. Although water authorities typically monitor water quality regularly, sudden events like thunderstorms can lead to overflow of wastewater or agricultural runoff, quickly degrading water conditions. Similarly, rising temperatures can speed up the growth of harmful microorganisms, making water quality more unpredictable. The four Hungarian locations tested in the study met EU water quality standards at the time of the research. However, the study suggests that these standards, while helpful, may not fully capture the risks associated with freshwater environments, which are more prone to sudden changes than seawater. The researchers advised swimmers to choose areas monitored by health authorities, avoid submerging their heads, rinse off after swimming, and be cautious of water temperature — as warm, stagnant water can encourage the growth of harmful bacteria.