All or parts of the Murray-Darling Basin Plan may be unlawful under federal legislation, the lawyer heading a South Australian royal commission into the basin says.
Bret Walker, SC, is investigating alleged water theft and rorting by irrigators in upstream states and says there's a "real risk" the plan is unlawful.
In an issues paper, Mr Walker explained the legal issue was whether or not the Water Act allows for social and economic outcomes to be considered in determining an environmentally sustainable level of take (ESLT).
It comes as farmers, fishers and environmentalists gathered at the Murray Mouth in regional South Australia on Tuesday, to protest against proposed changes to water allocations.
Protesters are warning against the reforms to be voted on in the Senate next week, which would divert 650 gigalitres from the Murray-Darling Basin to industry.
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"Big irrigation companies taking unsustainable amounts of water from the Murray-Darling Basin is a disaster," said Director of the Wilderness Society SA, Peter Owen.
Local advocate body, the River, Lakes and Coorong Action Group, said they were doubtful any change in industrial water allocation levels could deliver the same environmental benefits.
"This real water is to be replaced by projects that will supposedly deliver equivalent environmental benefits, but there are doubts about how effective they will be," spokeswoman Elizabeth Tregenza said.
