Water enforcement in NSW became so depleted that by mid-2016, the entire state had fewer compliance staff than the City of Canada Bay had parking inspectors, the Ombudsman said in a report that has prompted calls of a cover-up.

In a scathing assessment, the Ombudsman on Wednesday revealed details of four investigations of the sector since 2009 – none of which had been made public previously. The lack of disclosure came even though their repeated recommendations for change "did not always occur".

"It's a pity we didn't get this out a hell of a lot earlier," John McMillan, acting NSW Ombudsman, told Fairfax Media. Disclosing the industry's compliance issues sooner may have prevented them becoming "as deep and explosive" as they are now, he said.

The Ombudsman's latest investigation began in June last year after a number of staff within the Department of Primary Industries approached it out of concern the Strategic Investigation Unit – itself set up in the wake of the Ombudsman's first probe – was being "rendered ineffectual".