Authorities are blaming the mass death on a toxic algae bloom due to changing weather conditions.
It's the second incident of mass fish death along the Darling River since 10 000 fish died in December.
Officials said that a sudden cooling of the temperature over the weekend killed a pre-existing algae bloom in the area.
It resulted in the decomposing algae draining oxygen from the river.
KEEP UPDATED on the latest news by subscribing to our FREE newsletter.
- FOLLOW News24 on Twitter