A NSW government minister has been accused of snubbing farmers and residents gathered in the state's far-west to confront him over an environmental "disaster" that is believed to have killed up to a million fish.

Fisheries and Regional Water Minister Niall Blair travelled to Menindee, near Broken Hill, on Wednesday to investigate the algal blooms responsible for the mass fish deaths, including the large and critically-endangered Murray cod.

A shocking video posted by farmers from nearby Tolarno Station, on the banks of the Darling River, showed the water lined with dead Murray cod said to have been up to 100 years old.

"They have survived that many droughts, and the highs and lows of it all, but the one thing they haven’t been able to survive is this mismanagement," said Kate McBride, a farmer at Tolarno who filmed the video which has gone viral.