The Berejiklian government ignored warnings by an auditor for two years that it in needed to address rising salinity at Sydney's main reservoir, a delay the Labor opposition describes as "frankly shocking".

As Fairfax Media reported last year, the triennial audit of Sydney's water drinking catchment found salinity levels at Lake Burragorang had risen over a 20-year trend, and were twice the level of other catchments. Coal mining, a key source of those salts, was having a "cumulative and possibly accelerated" impact.

Lake Burragorang, behind Warragamba Dam, Sydney's main reservoir. Credit:Jonathan Ng

However, a report into pollution of the catchment, released by the Auditor-General last week, said despite the 2016 audit's call for an investigation into the source and implication of the salinity in the basin behind Warragamba Dam, nothing had been done.

Of the three public authorities now responsible for water quality at Lake Burragorang, the Auditor-General recommended the NSW Environment Protection Authority review the impact of licensed activities on water quality and develop strategies to improve water quality by June 30, 2019.