Wellington officials are pushing for an investigation into the city's wastewater infrastructure

Beaches south of the capital have been closed since a sewerage leak from Moa Point's treatment plant spilled onto the shore.

Repairs are underway, and discharge is now flowing into Cook Strait through a longer outfall pipe, but water on the coast remains unsafe.

Wellington Water Chair Nick Leggett says an independent inquiry is needed to unpack what went wrong.

He says these failures can be complex, and require thorough understanding.