The warning comes as heavy is forecast to hit the region next week.

Last month, a fault at the wastewater plant caused it to shut down, sending up to 70 million litres of untreated sewage into the sea each day.

The New Zealand government will publicly release the findings of an inquiry into the catastrophic failure of the Moa Point wastewater plant next week. This comes just over five weeks after a massive backflow of sewage flooded the plant, which has been discharging millions of litres of raw sewage into the Cook Strait daily since February.

A preliminary report into the Moa Point wastewater treatment plant will not be made public while the crown review is taking place, Wellington Water says.