The effects of the drought have begun appearing in streams and ponds.
Auckland Council's Pollution Response hotline is taking more calls from people reporting stagnant black streams, watercourses turning orange or red, and algal blooms.
It says prolonged periods of dry weather can have a major effect, but things should go back to normal once there's been a few days' rain.
People can help limit the flow of pollution to drains by washing their cars on the grass, and not pouring things like left-over paint down the drain.
