Public health authorities in Canterbury are warning of toxic algal blooms in Lake Forsyth.
The lake, also known as Te Roto o Wairewa, is a customary lake on Banks Peninsula managed by a Ngāi Tahu rūnanga.
The lake is prone to algal blooms.
The Canterbury District Health Board (DHB) said the potentially toxic blue-green algae was dangerous to people and animals, particularly dogs.
The DHB said no-one should drink the water, even if boiled, nor eat fish or shellfish from the lake until the warning was lifted.