Taylors Mistake Surf Life Saving Club announced the closure on its Facebook page on Sunday.
Christchurch City Council placed signs on Taylors Mistake Beach at the weekend, warning people the water was polluted and to avoid contact.
Said a Taylors Mistake Surf Life Saving Club spokesperson: "The water at Taylors Mistake beach and Hobsons Bay has been declared unsafe for swimming over the weekend, due to a sewerage outfall incident in Hobsons Bay."
"Only an advisory patrol is in place," the spokesperson said.
A council team will be closely monitoring the site.
The council's website states a damaged pipe caused the overflow.
"Pollution may take up to two days to completely clear after the discharge has ceased," it said.