In June, officials found the rocks had blocked off a section of Fraser River in British Columbia, stopping the salmon from swimming upstream to spawn.
Rescuers have spent weeks devising a plan to fly the fish by helicopter to a spot on the other side of the rockfall.
Conservationists warn the fish need to be able to lay their eggs, or the local salmon population will be at risk.
It is not known exactly how many fish are stuck, but it is believed that only 700 have managed to pass through the area affected by the rock slide without help.
Many of Canada’s First Nations indigenous peoples rely on the salmon for food and ceremonial purposes.
Jonathan Wilkinson, minister for Fisheries, Oceans and the Canadian Coast Guard, said the government had been “working around the clock” to help the fish.
Officials have not said when the airlifting will begin.
How will the rescue work?
Crews are now constructing a holding pond for the salmon.
The fish will then be transferred from the pond into 780-2,700 litre tanks, before a helicopter moves them away from the landslide.
The water in the tanks will be oxygenated, to help keep the fish calm.
While the holding pond is being built, workers are tagging the salmon in order to track their journey afterwards.
Crews have also tried to move larger rocks around to make it a bit easier for the fish to pass through themselves, as well as to remove rocks from the nearby cliff face that could prove dangerous for the people working there.