A serious water quality issue in the lower South Island

E-coli has been found in water bores in the Lower Waitaki plains...affecting a number of properties north of Oamaru.

Southern DHB Medical Officer of Health Dr Keith Reid says people whose drinking water comes from private bores should assume it's contaminated.

E-coli is a type of faecal bacteria, and affected water will need to be treated through boiling or chlorination.

Letters are being sent to dozens of properties which use bores.