Hundreds of dead eels and fish have been found in a creek in Christchurch.
Steve Firth, of Enviroment Canterbury, says staff found around 800 dead eels and fish in a four kilometre stretch along Kaputone Creek, in Belfast on Wednesday morning.
It is thought the source of contamination that killed the fish is either storm water or someone dumping something in the water.
There are no links to any industrial premises in the area, Mr Firth says.
ECAN staff visited the site to carry out waters on Wednesday and will be collecting more samples on Thursday.
Canterbury Medical Officer of Health Dr Ramon Pink advised people should keep out of the water, and ensure their pets don't go in if they're in the area.
If people have been in the water or have health concerns he suggested they contacted their GP.