Hundreds of thousands of fish have died in the Darling River at Menindee, the second such event in three weeks, in what Niall Blair, the fisheries minister, described as "an environmental catastrophe".

Graeme McCrabb, a Menindee resident who was again among the first to raise the alarm, said the latest die-off could be "worse than last time".

The extent of the latest fish kill on the Darling River at Menindee, as of Tuesday morning, January 29. Credit:Graeme McCrabb

"It's started off bigger than three weeks ago," Mr McCrabb told the Herald on Monday.

While the great bulk of the dead fish were bony herring, "golden and silver perch are starting to come up to die", he said. "The water's really black and dark – you couldn't see any joy there."