Fishery authorities were heading to the lower Murrumbidgee River on Tuesday afternoon to investigate reports of another fish kill on NSW rivers.

The Minister for Primary Industries, Niall Blair, who was himself visiting the site of a mass fish die-off on the Darling River at Menindee, said "we think it's in the hundreds to the thousands" at the Redbank weir pool near Balranald.

Perch are among the fish to have been killed in the Murrumbidgee fish kill. The image was taken at the site of another event this week at Menindee on the Darling River. Credit:Graeme McCrabb

"We think it's mostly carp and golden perch" with some bony herring, Mr Blair told the Herald after meeting Menindee locals seeking help after the region was hit by its third large fish kill in about five weeks.

"To see it first hand, it's important," he said, adding, "this is something that won't leave your memory for a long time."