NSW Primary Industries minister Niall Blair has dismissed criticism in the Murray-Darling Basin Royal Commission's final report he had used "crude language" and displayed "grossly irresponsible" behaviour after visiting the site of a massive fish kill on the Darling River.

Bret Walker SC, the SA Royal Commissioner, called for an overhaul of the $13 billion basin plan, claiming "maladministration" and "politics rather than science" had effectively made it "unlawful".

Some of the thousands of dead fish in the Darling River near Menindee in the second of three mass fish kills in the spate of about five weeks. Credit:Nick Moir

The 746-page tome, though, also considered the recent fish die-offs near Menindee in far-western NSW.

It said Mr Blair had used "crude language" by telling locals earlier this month that to cancel a planned project to divert some of the future flows from the nearby Menindee Lakes would "blow up" the basin plan.