Locals have woken up to a thick blanket of dead fish over sections of the Darling River in NSW's far west, as the toll from the latest mass kill continues to rise.
Officials on Monday found hundreds of thousands of dead fish in the Menindee weir pool and neighbouring waterways, including bony herring, golden perch and carp.
Regional Water Minister Niall Blair is expected to visit the region on Tuesday, having described the latest fish kill as an "environmental catastrophe".
He warned that conditions in the Darling River could deteriorate further, given the significant number of fish seen gasping for air.
Menindee tourism operator Rob Gregory on Tuesday morning posted footage of the river on Facebook, noting there were now "heaps and heaps" of silver perch among the dead.
"It's shocking this morning," he said.
"It's just a waste. An absolute waste."
Pictures show a large section of the river completely covered in small, floating dead fish.
Broken Hill man Travis Casey posted a video on Monday from a boat driving past hundreds of dead fish.
"Words don't really do it justice," he said.
"It's not bubbles or foam or algae, it's fish. Twenty-odd river kilometres of it."
The NSW Department of Primary Industries says the deaths are the result of critically-low levels of dissolved oxygen, likely linked to the mixing of weir pool water following a drop in temperatures in recent days.
The conditions are similar to that when up to a million fish were killed in the river about three weeks ago.
