With the summer holidays now here, many Brits will be looking to pay a visit to the local pool or lido.
But swimmers be warned – as public pools and water parks could be riddled with germs that can trigger a range of health issues, an expert has warned.
It means a quick dip could spark a bout of diarrhoea, an itchy rash or a condition known as swimmer’s ear – ruining summer plans.
While you might be reassured by a strong smell of chlorine, the chemical doesn’t work instantly and it doesn’t kill everything, according to a microbiologist.
‘On hot summer days, few things are more refreshing than a dip in the pool,’ Lisa Cuchara, a professor of biomedical sciences at Quinnipiac University in Connecticut, wrote on The Conversation.
‘But have you ever wondered if the pool is as clean as that crystal blue water appears?’
Professor Cuchara studies how germs spread in public spaces and said the ‘ick-factor’ of communal swimming spaces ‘does have some merit’.
So, will her warnings put you off your next planned swim?
Substances such as sweat and urine – which are commonly found in pool water – interact with chlorine to form chemical by-products called chloramines that may pose health risks, Professor Cuchara said (file image)
Over the last 25 years, swimming pools have been the most common setting for outbreaks of waterborne infectious intestinal disease in England and Wales, figures show.
The biggest culprit is Cryptosporidium, a parasite that can cause a stomach bug which lasts up to two weeks.
‘Even in a pool that’s properly treated with chlorine, some pathogens can linger for minutes to days,’ Professor Cuchara said.
‘One of the most common culprits is Cryptosporidium, a microscopic germ that causes watery diarrhoea.’
She said the germ spreads when faecal matter enters the water and is swallowed by another swimmer.
Even a tiny amount, invisible to the naked eye, can infect dozens of people, she said.
The Pseudomonas aeruginosa bacteria is another common germ that can cause issues such as hot tub rash – a skin infection that appears as a red, itchy bumpy rash that develops around hair follicles.
It can also trigger swimmer’s ear, an infection of the outer ear canal often caused by bacteria or fungi growing in the ear canal after water gets trapped there.

Cryptosporidium is a parasite that can cause a stomach bug which lasts up to two weeks. It is the main driver behind waterborne infectious intestinal diseases in England and Wales (file image)
Norovirus, commonly known as the stomach bug, and adenovirus, which typically causes cold or flu-like symptoms, can also linger in pool water and cause illness, she said.
A strong chlorine smell could also be cause for concern.
Substances such as sweat and urine – which are commonly found in pool water – interact with chlorine to form chemical by-products called chloramines that may pose health risks.
‘These byproducts are responsible for that strong chlorine smell,’ Professor Cuchara added.
‘A clean pool should actually lack a strong chlorine odour.
‘It’s a common myth that a strong chlorine smell is a good sign of a clean pool. In fact, it may actually be a red flag that means the opposite – that the water is contaminated and should perhaps be avoided.’
Tips to help prevent yourself falling ill include trying to keep water out of your mouth, showering after swimming and drying ears thoroughly.