Summer's here – which means more sun, surf and swimming. Your local aquatic centre can get more crowded than the shops during Boxing Day sales.

But it's not always safe to go into the water. Health authorities, such as NSW Health, strongly advise people to avoid swimming in pools if they have, or have recently had, diarrhoea.

Diarrhoea and cryptosporidiosis

Diarrhoea can be a symptom of cryptosporidiosis, an infection of the bowel caused by the parasite Cryptosporidium. Other symptoms can include stomach cramps, fever, nausea and vomiting. People who are infected with Cryptosporidium can contaminate pools and it takes very high levels of chlorine used over several days to kill the parasite. And it can be spread by infected individuals for up to 14 days after the last symptom.

You should wait at least 2 weeks after you have fully recovered from diarrhoea and symptoms have disappeared before you take a dip into a public pool. This will help you avoid spreading the disease to other people.

Other swimmers can become infected by swallowing a very small amount of pool water if it contains Cryptosporidium. This brings on diarrhoea a few days later.

It's peak season

Reported cases of cryptosporidiosis tend to peak between November and March.

Dr Jeremy McAnulty, Director of Health Protection at NSW Health, says people of all ages, but particularly parents and carers of young children, should take steps to prevent the spread of the infection.

“Cryptosporidiosis is easily spread from person to person in swimming pools, splash parks, interactive fountains, spas or jacuzzis,” Dr McAnulty explains.

“We usually see cases increase over summer and there have been plenty of outbreaks caused by contaminated swimming pools."

Other risk factors include contact with farm animals and drinking untreated water.

How to prevent cryptosporidiosis

To help prevent the spread of cryptosporidiosis and to avoid getting infected by the parasite, people are advised to:

• wash your hands thoroughly with soap and running water after using the toilet or handling animals
• avoid swallowing pool water
• avoid swimming in a pool until at least 2 weeks after you have completely recovered from diarrhoea
• avoid drinking untreated water from creeks, rivers and dams when camping or bushwalking – bringing water to a rolling (rapid) boil should kill these parasites

Parents can also:

• take their children to the toilet more frequently to avoid accidents in the pool
• dress children who are not toilet trained in swimming nappies or tight-fitting, waterproof pants
• change nappies in a bathroom and not on poolside decks
• wash children thoroughly (especially on the bottom) with soap and water before going swimming
• wash their hands thoroughly with soap and running water after changing a child’s nappy

Contact your GP if you are concerned about any symptoms. If they're not available, call healthdirect on 1800 022 222 to speak with a registered nurse (known as NURSE-ON-CALL in Victoria).