A retrospective law change by the Newman Government in Queensland that helped a major Liberal National Party donor avoid prosecution would have been investigated in New South Wales, says the former head of that state's anti-corruption body.

David Ipp, the commissioner of the NSW Independent Commission Against Corruption (ICAC) until his retirement in 2013, told the ABC it was "odd" that there had been no probe by Queensland authorities into a last-minute change to river quarrying laws that appeared to favour Karreman Quarries, a significant LNP donor.

The ABC revealed in June that Karreman Quarries had been facing prosecution for quarrying deemed illegal by Natural Resources Department officials, who were gearing up to take the company to court.

But in an eleventh-hour amendment that passed through the Parliament unnoticed and without debate, the LNP Government made all of Karreman's activities since 2010 lawful.

The change to the law meant officials were no longer able to prosecute the company.

"In my opinion, if that were to have happened in New South Wales, then the ICAC would at least investigate to see if there was corruption," Mr Ipp said.

The amendment was drawn up on the orders of Deputy Premier Jeff Seeney, who when later interviewed by the ABC could not name any other company or individual that would benefit from the change.

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Quarrying caused erosion, loss of prime lands, farmers say

Mr Ipp said retrospective legislation was highly unusual and was "usually justified as something that was absolutely necessary for the public good".

"As I understand it, this retrospective legislation is primarily for the benefit of a single individual or single company. That makes it extraordinary," he said.

"If then this individual or company is a major donor to the political party concerned, well that really does give rise to some suspicions."

The change to the law allowed Karreman Quarries to continue extracting sand and gravel from the Brisbane River at Harlin, a business worth more than $15 million a year to the company.

Local farmers have complained for 20 years that Karreman's activities had caused erosion of the riverbank and the loss of prime land on their properties, which lie upstream of the quarrying works.

Fluvial geomorphologist, Professor John Olley of Griffith University, told the ABC Karreman Quarries' disturbance of the river banks triggered upstream erosion and the company was "in effect mining farmers' properties upstream".

An Australian Rivers Institute report said in 2007 the extraction was unsustainable and should cease altogether.

It warned that it flushed excessive sediment into Wivenhoe Dam, the main source of drinking water for Brisbane, adding millions to the cost of processing.

Karreman Quarries one of LNP's largest donors

Since June, the Government has allocated $1.6 million of taxpayer funds for riverbank remediation at Harlin.

Mr Seeney has said it had always been LNP policy to unwind previous Labor government's 2010 reforms changing the definition of watercourses, which had led to the attempt to prosecute Karreman Quarries.

But the ABC uncovered documents showing officials were caught off guard by the government's planned amendment and a senior aide to Mr Seeney even drafted a letter for him to sign in March warning the quarry owner that he was operating without a permit.

It was never sent.

Karreman Quarries has given $75,000 to the LNP in recent years, making it one of its largest donors.

Mr Seeney has denied his ordering of the change to the law had anything to do with donations by Karreman Quarries to the LNP, saying it would be wrong to stop a business that had been going for 20 years.

Mr Ipp launched the ICAC inquiries into former NSW government ministers Eddie Obeid and Ian MacDonald that led to corruption findings and revelations of widespread influence-peddling in that state by both sides of politics.

On ABC's 7.30 program earlier this month, he warned of diminishing political accountability in Queensland, singling out "cash-for-access" type fundraising events and a lack of transparency in political donations, saying they were corrosive to democracy.