But he has not ruled out its ability to land a "knockout punch" on native fish in the Macquarie and other NSW rivers.

The president of Inland Waterways, who says native fish are already on the "back foot" because of man-made challenges, thinks fish kills are "almost guaranteed to occur" as summer advances.

"Inland Waterways will work closely with the state government to do everything we can," he said.

"But the reality is there is a strong likelihood that we will see hundreds of thousands if not millions of dead fish (in NSW) this summer because there is just no way that we have the resources or the ability to rescue and store all fish," Mr Hansen said.

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The president understands the Department of Primary Industries is "already working on a plan" to oxygenate water in refuge pools of the Macquarie River.

"That is our best chance of saving a significant number of fish," he said.

Mr Hansen said as releases from Burrendong Dam became "less and less", the river would turn into a series of refuge pools that "may not even be linked".

"The fish will be adversely affected by increasing temperatures, algal blooms and deoxygenation of the water," he said.

The Dubbo man said "all fish" in the Macquarie River were at risk including recreational fishing species the Murray Cod, Yellowbelly and Golden Perch, along with endangered species Trout Cod and Silver Perch.

"Even under good conditions we've almost wiped them out unfortunately," he said.

Mr Hansen, who served on former Primary Industries Minister Niall Blair's advisory council and has applied to do the same for Agriculture Minister Adam Marshall, says rain and the "opening of fish passage, screening of irrigation and off-take pumps to prevent fish extraction, and correcting of cold water pollution from large dams" would see growth in native fish numbers "long into the future".

But for now he says the goal is to "get them through to the cooler months next year".

Mr Marshall has launched a $10 million "modern-day Noah's Ark".

It encompasses artificial aeration, oxygenation and chemical treatment to support water quality; an "unprecedented" breeding program at government and private hatcheries; dedicated teams to rescue and relocate fish, and the state's largest restocking program of rescued and bred native fish once "normal water conditions return".

Teams are currently working on the Darling River at Menindee.

State Member for the Dubbo electorate Dugald Saunders has warned that when rain comes it can generate "black water" from dry creek beds.

It includes undissolved organic matter and no oxygen which also kills fish, he says.

"The reality is we can't control mother nature and this (fish kills) has happened for centuries," he said.

"It's just that we are more aware of it then ever."

Mr Hansen remains ever optimistic about the survival of native fish in a "land of drought and flooding rain".

"They can, they have before and will have to again," he said.