New Zealand's biggest tourist draw Queenstown is under a boil water notice after several cases of illness-inducing cryptosporidium cases were identified.
Residents and tourists at the ski resort, adventure sport and luxury shopping destination have been asked to treat their water supply.
Authorities are not yet sure whether the public water supply is the source of the outbreak but the notice has been issued as a precaution.
Queenstown Lakes council spokesman Tony Avery said it was the first cases of the diarrhoea-inducing parasite for 40 years.
"We're taking advice from the public health (authorities) around that," he said.
"The source of these cases is not yet known."
A council statement links social media posts of people feeling unwell to the Fernhill suburb, south of the main centre, and has upped testing in the area.
The parasite cryptosporidium lives in the gut of infected humans and animals, according to the US Center for Disease Control and Prevention, and spreads through faeces.
Symptoms show an average of seven days after infection, and is typically watery diarrhoea.
Prime Minister Chris Hipkins said the outbreak was still being investigated.
"They've seen a number of presentations with people who are unwell. They're still trying to identify where that has happened and are working on the basis it may have come through the water," he said.
New Zealand has a long history of poor water treatment and outbreak linked to underinvestment in water and wastewater infrastructure.
Reform of the sector has been a major issue during the last term of parliament, with the Labour-led government attempting to regionalise control of water assets against stark opposition.
