Former NSW chief scientist and Natural Resources Commissioner Professor John Williams also blasted authority chair Craig Knowles for quoting the late Professor Peter Cullen - one of Australia's most influential water scientists - in a speech that dismissed scientists critical of the plan as ''lobbyists''.

Professor Williams, who collaborated with Professor Cullen on national water research for more than two decades, described use of the quote as '' a dreadful insult'' to his colleague's scientific legacy.

''I knew Peter very well, and if he was alive today, he would be tearing strips off this plan for not being peer reviewed. He was a fearless advocate for scrupulous, well-analysed science, and would be appalled by the manipulation of science being used to push this plan through,'' he said.

Professor Cullen, a charismatic and outspoken figure in the national water reform debate, was awarded the Prime Minister's Prize for his work in shaping a national action plan for salinity and water quality. He died at his Canberra home in 2008.

In a speech to the Farm Writers Association of NSW in Sydney, Mr Knowles quoted Professor Cullen to support criticisms of the Wentworth Group of Concerned Scientists - a national science think-tank of which Professor Cullen was a founding and prominent member.

Current members include Professor Tim Flannery, water economist Professor Mike Young, environmental business philanthropist Rob Purves and former federal policy adviser Peter Cosier.

''I am fond of quoting the late Professor Peter Cullen, who will be known to many of you as one of the founders of the Wentworth Group who, in their current form, have taken an active role as one of the many lobby groups in the debate about the plan,'' Mr Knowles said.

He quoted Professor Cullen as saying scientists ''should not expect their scientific standing gives them any special right to decide value questions for society.

''Their science needs to inform the debate, not replace the debate''.

Ironically, the quote is taken from a speech in which Professor Cullen urged scientists to ''speak truth to power'' and engage in public debate on environmental issues.

Mr Knowles said he challenged ''any assertion that the draft plan isn't based on firm science''.

The plan had been peer-reviewed by ''a panel led by CSIRO and they determined [it] was sufficient as a basis to make a start,'' Mr Knowles said.

Friends of the Earth water policy spokesman Jonathan La Nauze said environment groups also rejected the science underpinning the draft plan ''for one simple reason - because the [authority's] modelling shows it would fail to achieve its fundamental goal - a healthy working river,'' he said.

During a Senate hearing last week, Mr La Nauze submitted a study showing the plan would fail to meet almost 50 of its own ecological targets.