Queenstown is under a boil water notice after several cases involving an illness-inducing parasite

Residents and tourists have been asked to treat their water supply.

Authorities are unsure 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 says it's the first cases of the diarrhoea-inducing parasite for 40 years.