The findings of South Australia's royal commission into Murray-Darling Basin could be compromised by federal government interference, SA-BEST MLC Frank Pangallo says.
The royal commission will hold its first public hearings on Monday, but the federal government has started High Court action to stop its staff and those at the Murray Darling Basin Authority from giving evidence at the enquiry.
"It is a disgrace that the Royal Commissioner Bret Walker may not be able to call for evidence from senior federal government and Basin Authority personnel, the very people he needs to hear from to get to the bottom of these serious allegations," Mr Pangallo said.
In a joint statement, the Commonwealth and Basin Authority said the inquiry did not have the power to compel witnesses.
"The Commonwealth and MDBA's view is that the royal commission cannot compel the Commonwealth or the MDBA to provide documents or give evidence."
The royal commission was established in January 2018 to inquire into the operations and effectiveness of the basin plan after widespread reports of water theft.
Its final report is due by February next year.
Mr Walker has already consulted with communities across the river system and visited key basin sites, and received more than 100 written submissions.