A health warning has been issued for part of the Selwyn/Waikirikiri River after high levels of potentially toxic blue-green algae were found.
Canterbury District Health Board is advising people to stay away from the river at Coes Ford until the health warning has been lifted. Animals, particularly dogs, should also be kept away
Medical Officer of Health Alistair Humphrey said the algae formed what looked like dark brown or black mats and could produce toxins harmful to people and animals.
Reticulated town water supplies are safe but no one should drink the water from the river at any time.
Canterbury Regional Council is monitoring the sites and will advise of any changes in water quality.