1. Antibiotic-resistant bacteria

Traces of antibiotics can enter the sea through human and animal waste, affecting the organisms that live there, says Professor Dearbháile Morris, leader of the University of Galway PIER Project, a public health study that examines exposure to antibiotic-resistant bacteria in recreational waters.

”When bacteria are exposed to antibiotics, they do things to try and make sure that they can survive…they can become resistant to antibiotics,” says Morris.

While antibiotic-resistant (AR) bacteria aren’t an issue for most people, they could be dangerous if passed to vulnerable people, such as babies or older adults.

The PIER Project compared 150 people who regularly use recreational water with 150 non-users to see if they are more likely to carry AR bacteria in their gut. “What we found was that those who used water a lot were less likely to be carrying antibiotic-resistant bacteria,” says Morris.

This could be because water quality is high in Ireland, or because people who regularly spend time in the sea have overall better health, says Morris. “The theory is that people who engage in high levels of recreational water activity overall potentially have a healthier lifestyle than others.”

2. Escherichia coli (E. coli)

E. coli is a bacterium found in the intestines of humans and animals, and can enter the seawater through contamination from sewage, agricultural runoff, or after heavy rainfall. While most strains are harmless, specific pathogenic strains can cause severe illness, explains Dr Linda Holland, associate professor of microbiology at Dublin City University.

“E. coli is an important indicator organism in measuring water quality. The presence of high levels of E. coli ‘indicates’ a possible faecal contamination event and a health risk for swimmers. Potential health effects include diarrhoea, vomiting, stomach cramps and fever.”

3. Intestinal enterococci

Intestinal enterococci are bacteria found in the intestines of humans and animals. They can be associated with gastrointestinal illness, ear infections, eye infections, and skin infections. “They can survive longer than E. coli in seawater and are considered one of the best indicators of faecal pollution. For this reason, intestinal enterococci are the second indicator microbe that is used to monitor water quality,” says Holland.

4. Norovirus

This highly infectious virus causes vomiting, diarrhoea, stomach pain, and fever. “It does not live naturally in open seawater. However, it can become a localised hazard if a major, untreated municipal sewage overflow occurs near a bathing area,” says Holland.

5. Cryptosporidium

Cryptosporidium is a parasite found in animal and human faeces. It’s more commonly associated with freshwater and drinking water than seawater, but can enter coastal waters through sewage discharges directly into the water, says Holland. “Potential health effects include severe diarrhoea, abdominal pain, and dehydration.”

6. Giardia

While the beach can be a lovely spot to walk your dog, it’s vital to clean up after it. Dog faeces carry harmful bacteria that can cause illness if they contaminate water.

“Dogs’ gut flora is very different to humans, so they can carry around organisms that aren’t normal to humans, but that can make humans potentially very sick. An example of that would be a protozoan parasite called Giardia. [The resulting intestinal infection] Giardiasis can cause a diarrheal illness in humans,” says Morris.

While alcohol-based hand gel kills most bacteria, soap and water are the only way to eliminate Giardia. Morris suggests bringing “a refillable bottle of water to the beach and some hand wash”.

Monitoring water quality

Water is tested once a month in designated bathing areas in Ireland between June 1 and September 15 each year. It is overseen by local authorities, the Environmental Protection Agency (EPA), and the HSE. Some councils have started voluntary out-of-season testing, due to the rising popularity of year-round swimming.

Dr Jenny Deakin, programme manager at the EPA, says: “Heavy rainfall events are becoming more frequent during the bathing season, which brings an increased risk of contamination from runoff from wastewater, urban, and agricultural sources.

“These conditions can result in short-term pollution, which increases the risk to people’s health while swimming.”

When a pollution incident occurs, local authorities apply a swimming restriction at the bathing water, says Deakin. “The restriction stays in place until water sampling shows that the water quality has returned to normal.

“Swimmers should always check beaches.ie, and signage at the beach, for the latest water quality information. They should remember to follow the 48-hour rule, which is to avoid contact with open water for at least 48 hours after heavy rainfall to protect health.”

The good news is that water quality remains high in Ireland. According to the EPA, 98% of designated swimming sites (150 of 153) met or exceeded the minimum required standard in 2025.

Tips for avoiding beach bugs

• Before Swimming:
  Check the water quality at the beach. The best source is beaches.ie, which provides information on current bathing water status, advisories, restrictions, and water quality classifications.
  Check the weather. Avoid swimming for 24–48 hours after very heavy rainfall.
• While Swimming:
  Try not to swallow seawater.
  Avoid swimming with open wounds or significant skin infections.
  Stay away from sewage outfalls, drainage pipes, discoloured water and any water with strong sewage odours.
• After Swimming:
  Shower after swimming to reduce the risk of skin and ear infection, or eye irritation.
  Wash your hands before eating.