Concerns an outbreak of cryptosporidium stemmed from a Canterbury public swimming pool complex

Health New Zealand's investigating the outbreak after 18 cases of the gut parasite were identified in Selwyn in the past week.

All but four had direct contact with the pool.

Medical officer of health, Dr Cheryl Brunton says the complex's water quality and disinfection dosages complied with the relevant standards.

She says the available chlorine was raised overnight as a precaution.