It's clear waters ahead for Sydney's east coast, where sewage pipes that dump wastewater into the ocean are set to be switched off by the NSW government.

Three outfalls at Vaucluse and Diamond Bay – the last pipes in the state that release untreated sewage into the water – will be closed and redirected to the Bondi Wastewater Treatment Plant, Premier Gladys Berejiklian announced on Sunday.

Diamond Bay, where one of the last three ocean sewage outfalls in the state will be closed. Credit:Wolter Peeters

The government predicts that the $86 million project will be finished in 2020, with geotechnical tests set to begin in the middle of next year before digging and the construction of new tunnels can start.

A report commissioned by Sydney Water earlier this year found that visible plumes from the sewage outfalls posed critical health risks, with bacteria analysis showing that the area was not suitable for swimming.