The Murray-Darling Basin Authority has hit back at criticism it takes a robotic approach to implementing the plan to carve up water across the river system.
Nationals senator Bridget McKenzie said farmers on the ground and representative bodies were concerned about the authority's lack of flexibility.
"This blind adherence and almost robotic approach to implementing the MDB plan is causing frustration in communities and with irrigators themselves - and others," she told a Senate hearing in Canberra on Tuesday.
MDBA chief executive Phillip Glyde said the organisation was hearing similar criticism in more strident terms.
But he defended the authority, arguing changes to the plan needed to gain approval from basin governments and parliaments.
"One of the great strengths and one of the great weaknesses of the basin plan is that it provides certainty through legislation," Mr Glyde said.
"That makes it from time to time quite hard to change."
He said the lack of frequent major changes were not down to the basin authority's intransigence.
"I'd reject the criticism that the basin plan doesn't change. Changes have been made over the last eight years, all of which have required the agreement of governments that are party to it," Mr Glyde said.
"That's the great limiting step. In order to get change you've got to get everyone on board and that's hard in a contested space."
The MBDA chief noted criticism was coming from across a spectrum of interests including irrigators and environmentalists.
Senator McKenzie also probed the MDBA's efforts to split its compliance functions from enforcing the plan.
Despite the government first promising a substantive inspector-general role in October 2019, legislation is still being drafted.
Officials told the hearing discussions with state governments about the new compliance office were ongoing and the bill was expected to be introduced between July and September.
Water Minister Keith Pitt announced in September the inspector-general would take over policing water in the basin to avoid perceptions the authority could mark its own homework.
Former MDBA official Maryanne Slattery, who has been a strident critic of the plan's execution, reiterated her calls for a royal commission to address "manipulation" of water targets.
She told the hearing that "endless scandals" meant a royal commission was the only way to get all problems out in the open.
