Algae has been found in a Canterbury river and river users are advised to stay away.
The algae, which forms dark brown of black mats in the water, is in the Ashley river, near Rangiora.
Canterbury District Health Board has issued a health warning, saying the toxins are harmful to both people and animals, especially dogs.
Medical Officer of Health Alistair Humphrey said exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.
Dr Humphrey said those experiencing any symptoms should see a doctor immediately.