Creeks in the Upper Murray may take years to recover from a mass fish kill, with one fisherman comparing the water to oil.
Thousands of fish, including large natives, have been killed this week after rain flushed ash and debris into waterways.
Corryong man Ted Evans said the Cudgewa and Corryong creeks were both "knackered", while large numbers of fish had washed up dead as far away as Thologolong, upstream of the Hume Weir.
"Everyday your heart breaks a little more," he said.
"The rain came and everyone was a bit happy, but we all knew what would happen.
"It's worse than I ever thought it could be."
Mr Evans said it was unlikely any fish could have survived in the creek due to the water quality.
"It's like oil when you pick up the water," he said.
"All the banks are knee deep in mud, ash and silt.
"There are thousands of carp and hundreds of cod lining the banks wherever you go.
"It's just the icing on the cake after everything else that's happened over the last few weeks."
Another man said he was "lost for words" after viewing the damage.
Water quality alerts note there is low dissolved oxygen levels, high turbidity and bushfire contamination in waterways.
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Josh Read documented the damage on social media, with one photograph showing a large pile of dead cod pulled from the water.
"Some of the biggest cod I've seen in my life are dead in piles," he said.
"We didn't see any struggling or dying fish that could be rescued or relocated, only dead ones."
Corryong Angling Club treasurer Shea Bloom said the annual Cudgewa Fishing Classic, which would have been held at the end of February, has been cancelled.
"It's a catastrophic fish kill," Ms Bloom said.
"It's going to affect the whole ecosystem, but fishing is also a huge part of our tourism as well.
"Some of those big cod we found in the Cudgewa and Corryong creeks were over a metre long.
"They would be very old fish."
Ms Bloom said she had broken down in tears on the bank of the water after viewing the dead fish earlier this week.
"It's pretty devastating," she said.
"When you love and care for fish so much, it's heart wrenching."
The angling club has regularly restocked Upper Murray waterways.
A charity page to fund the restocking has been launched, and has raised nearly $5000.
Ms Bloom said there was little that could have been done to prevent the mass kill.
Some residents rushed down and saved a small number of native fish when the rain began to fall on Monday and placed them in dams.
A NSW Department of Primary Industries spokesman said waterways in the area had been "put under extreme stress".
"Staff have undertaken inspections and water quality monitoring and have been liaising with Victorian colleagues," the spokesman said.
"Water quality observations show oxygen levels have improved behind the initial flows, and while they are still below normal levels they are not causing further fish deaths."
Murray cod, golden perch, other native species, carp and redfin have been killed.
Victorian Fishing Association chief executive Travis Dowling said the agency would look to restock the waterways, and urged fishermen to return after the recovery.
The restocking could start in six to 12 months, he said, or longer depending how long the waterways take to recover.
"In the past when we've had really significant fires, the short-term impact is quite concerning, but longer term we know the rivers will recover," he said.
Drinking water hasn't been impacted.