North Shore City Council is warning residents in Northcote to avoid the water for at least 24 hours after a sewage pipe leaked on Friday afternoon.
Council spokesperson Blair Harkness says the overflow was spotted by engineers passing by who called in back-up support and made emergency repairs to the broken sewer line.
Mr Harkness says it is not known how much sewage leaked from the pipe, but tanker trucks diverted the flow into the Onepoto stream and into Shoal Bay.
He says boardsailers use the area to launch their craft, but there are no plans to put up warning signs.
The sewage is expected to be sufficiently diluted within 24 hours.