People are urged to be on the look out for polluted water signs along Christchurch's coastline

The city council has confirmed sewage has leaked into Pegasus Bay.

The affected waterways are believed to be around the Scarborough, Sumner areas.

A council spokesperson says in very wet weather or due to sewer blockages, they can't avoid discharging wastewater from nearby sewers into the river.

They say they will be checking the river banks for visible waste and monitoring water quality.

People should avoid affected waterways for at least 48 hours.