A highly contagious parasite that causes month-long diarrhoea has reached Australian shores.

Cryptosporidiosis can withstand chlorinated waters and is spread predominately in public pools, water parks, or by drinking contaminated water.

NSW Health issued a public health warning about the parasite after a slew of confirmed cases.

The disease can withstand chlorinated waters and is spread predominately in public pools, water parks, or by drinking contaminated water

Health officials said the parasite can be passed into the water ways through people who have recently had diarrhoea.

People were warned against swimming for two weeks after their symptoms are resolved to avoid contaminating pools and spreading the infection.

Case reports tend to peak between November and March, with the highest monthly notifications in the past five years in March 2017 with 325 cases.

Symptoms include lots of diarrhoea, stomach cramps, nausea and sometimes vomiting or fever. There is no specific treatment for the condition and symptoms may last a few weeks.

It can be passed into the water ways through people who have recently had diarrhoea

While the disease is most common in infants and children, adults are also susceptible.

Coming into summer, public pools tend to get overcrowded as families flock to them to a fun, family-friendly day out.

'If an infected person gets into a pool and another swimmer swallows even a small amount of pool water, they can get infected and will start experiencing diarrhoea a few days later,' health bosses said.

The disease has no treatment process, so those infected are told to stay at home and drink plenty of fluids to avoid dehydration.