Mr Minns travelled to Menindee on Wednesday to talk with local agencies and announce an inquiry after millions of fish died in the Darling River close to two weeks ago.

The fish kill, caused by low levels of oxygen in the water, had been catastrophic for locals in Menindee where the river offered huge potential for agriculture and tourism, the premier told reporters.

"In many ways it's a marvel of the world, but we need to make sure that we protect its waterways, particularly when there's an abundance of water," Mr Minns said, noting that it was the second major fish kill in the area in five years.

The government plans to get a sense of what lead agencies have been doing in the wake of the fish deaths and visit locals to learn how the disaster has affected them.

Local MP Roy Butler said the fish kills had been shattering for locals in and around the Darling River.

"This has been a devastating thing for the community. Seeing those images that made their way around on social media was devastating for everyone," he said.

"The community is looking forward to understanding what's happened here ... so we can try and avoid that happening again."

Environment Minister Penny Sharpe said the incident had caused huge concern among locals, including over whether they could drink their tap water.

"This is an ecological disaster but it is also a really serious matter for every single person who's in this community," she said.

"We have to look at all of the issues and it's very clear that the abundance of water led to an abundance of fish, particularly those bony herring.

"But, we have to look long-term around how the rivers are being managed. I'm not going make any bold predictions, but I think understanding and learning from this experience is very important."

A number of agencies have been involved in the clean-up, which is being co-ordinated by NSW Police.

The organisations, including WaterNSW and the Office of Environment and Heritage, have had to focus on maintaining drinkable water quality in Menindee while also trying to clean up the dead fish.

"We saw some pretty gruesome sites with regards to the fish on the water over a week ago," NSW Police emergency controller Brett Greentree said, adding the groups had to refine systems for cleaning up and disposing of the fish as quickly as possible.

"Hopefully this won't occur again downstream but if it does, we are certainly in a much better place to move quicker, be swifter with regards to our response," Mr Greentree said.

The fish are being disposed of at the Menindee dump.

Australian Associated Press