Unity among irrigators in the Murray-Darling Basin is beginning to fray with one large group in the southern region breaking ranks, dubbing the lack of monitoring of water use in northern areas as "insane".

The Southern Riverina Irrigators exited the NSW Irrigators' Council on Thursday - the same day the South Australian government released its royal commission report into the basin plan.

The 746-page tome detailed many criticisms including the weak measurement of so-called floodplain harvesting, leaving it "a virtually data-free zone" in parts of NSW and Queensland.

A southern irrigation group in the Murray-Darling Basin has broken ranks and criticised those in the north for leaving them to make water cuts for the environment. Credit:Kate Geraghty

Chris Brooks, chairman of the dissenting group of 1800 farmers, said he had withdrawn financial support for the peak irrigators' body - worth $65,000 a year. He said he hoped others would follow.