A Senate water reform inquiry has accused the federal Agriculture Department of ''talking rubbish'' in response to questions about changes to farm water licences under the Murray-Darling Basin Authority's draft water plan.
The rural affairs committee also heard the plan would not meet almost 50 ecological targets listed by the authority in its draft plan as essential to river health.
Tempers flared during the public hearing in Canberra yesterday, with accusations of verballing, arrogance and ''dodgy science''.
Department of Agriculture staff appeared flummoxed when asked which water licence categories were used in economic modelling supporting the plan. Responding to questions by NSW Liberal Senator Bill Heffernan, they struggled to describe differences between high and low security irrigation water.
''This is scary … you've got no idea what you're modelling,'' Senator Heffernan said.
Federal environment department deputy secretary David Parker angrily accused South Australian Greens Senator Sarah Hanson-Young and Senator Heffernan of ''verballing'' his answers. Senator Hanson-Young and the authority's chief executive Rhondda Dickson also clashed over questions on the draft plan's science.
''The plan is a dud, and you're asking us to sign off on it,'' Senator Hanson-Young said.
Friends of the Earth water policy spokesman Jonathan La Nauze told the inquiry Australia would lose at least eight globally important wetlands, including key waterbird nesting sites, if the plan was adopted.
Mr La Nauze tabled a study showing large areas of the basin would suffer ''permanent decline'', with widespread loss of native fish, wetlands and coolibah woodlands, as well as increased salinity levels.
Despite the volume of information produced by the authority, it had ''never published a simple summary of what the proposed plan means for the environment,'' he said.
''It took days of poring over some 20 authority publications, but this is what it looks like - what lives and what dies under the plan,'' Mr La Nauze told the inquiry.
The study shows the plan will fail to meet 48 specific ecological targets set by the authority as critical to river health. A further 36 targets would be in doubt. The study estimates the plan will fail to meet four out of five targets for the Murrumbidgee wetlands, with loss of waterbird breeding sites as well as turtles, frogs and native fish.
Mr La Nauze said at least eight of the basin's 16 internationally listed Ramsar wetlands would suffer ''such a significant decline that it would amount to a change of ecological character''.
This would put Australia in breach of its duties under the Ramsar agreement, which protect wetlands of global significance.
Australian Conservation Foundation spokesman Paul Sinclair also told the inquiry the authority was ''struggling to engage respectfully'' with conservation groups.
''They see us as opponents to be held at bay,'' Dr Sinclair said.
The Senate inquiry is investigating the potential impacts of the authority's draft water management plan, which will introduce a new water management regime for Australia's major food production region.