Fisheries staff from the NSW Department of Primary Industries will rescue as many Murray Cod and Golden Perch as possible from about 20 pools of water that are close to drying out.
Rescued fish will be transferred from nets into vehicles with oxygen and temperature control to provide the best possible chance of survival.
The fish will then be taken to a section of the Lower Darling which fishery experts say will offer better quality habitat and long-term water security for the fish.
Hundreds of thousands of fish were killed in January along a stretch of the Lower Darling River,which followed an incident before Christmas where an estimated 10,000 fish died.
Mr Marshall said NSW was facing what the Bureau of Meteorology considers to be the worst drought on record. There are fears this year's fish kill could dwarf the mass die-offs last summer.
"This summer is going to be nothing short of fish Armageddon,"Mr Marshall said.
"It’s absolutely critical we get on the front foot while we still have the chance to rescue and relocate as many fish as possible.