Officials from the federal and provincial governments are preparing to use helicopters to fly salmon over a rock slide on the Fraser River to their spawning grounds upstream.

The strategy is one of several approaches officials are taking to try to mitigate the effects of what has become known as the Big Bar rock slide north of Lillooet.

The slide was discovered in late June, though it likely occurred sometime in late October or early November, according to the B.C. provincial government.

The incident created a five-metre waterfall that's preventing many fish from swimming upstream to spawn.

In order to help salmon get up to their spawning grounds, crews have built a holding pond below the rock slide. Salmon will swim through a one-way gate, or weir, into the pond where they'll be netted, tagged, and placed in oxygenated aluminum tanks.

The tanks will then be flown by helicopter upstream of the slide where the fish will be released back into the river.

Andrew J.L. Thomson, regional director for the federal Department of Fisheries and Oceans Fisheries Management Branch, told CTV News the helicopter strategy is a temporary solution that officials are working on in parallel with other, longer-term efforts.

"There are limitations as to how many fish, of course, we can move at any one time using a helicopter," Thomson said. "Nevertheless, it's a start to try and get some of those fish up there while we're pursuing the other options."

At the same time, crews are also working to secure the rock walls of the canyon so that the riverbed can be further manipulated into a "natural fishway," Thomson said.

"We're also pursuing development of fish ladders that we can insert into the system," he said. "Those ladders are being designed and built so maybe there's a possibility of getting these artificial fish ladders placed into the system if our movement of the rocks is not as successful as we want."

The efforts are a race against time. While chinook salmon are already making their way up to the blocked part of the river, their numbers are much smaller and more manageable than the expected sockeye run, which is due to arrive around mid-August, Thomson said.

"We expect over three million sockeye to want to migrate north of that rockslide," he said. "When you get into that number of fish, then you have to find alternate methods."

Transporting millions of fish upstream by helicopter isn't realistic, Thomson said, but the effort to move chinook salmon by helicopter will be an important test to see how effective the strategy can be.

"We think we can move a significant number of those fish, but that's the trial that we'll have to go through," he said. "How many fish can we attract into this holding pond? How many fish can we transport by the buckets up and then release them?"

Those questions will begin to be answered on Monday, and their answers will have implications for the other work being done at the slide site.

The provincial and federal governments say they've made a joint commitment to do everything possible to make sure chinook, steelhead, coho and sockeye are able to reach their spawning grounds.

With files from the Canadian Press