LILLOOET, B.C. -- Government officials say there is a “high risk” they won't be fully successful in rescuing salmon species threatened by a massive landslide on British Columbia's Fraser River.

The landslide at Big Bar northwest of Kamloops was discovered in June and the government has said several species are at risk of extinction.

In a progress update Wednesday, Sarah Murdoch of the Department of Fisheries and Oceans says water levels are beginning to drop on the river, presenting the only opportunity to remove enormous amounts of rock blocking salmon migration routes before spring and summer runs arrive.

She says there will likely only be a window open until mid-March when the flow is low, but officials are also facing difficult winter conditions in the remote area.

The government issued an open request for information to the private sector on Nov. 26 and is accepting responses through Friday.

Murdoch defended the government's posting of the request so late in the year, saying it's not the only effort the government has made to engage with the private sector to clear the slide.

Experts from various levels of governments, agencies and the private sector have all chimed in, including through an “innovation tracker” and an expert panel, she says.

“All of that information has also been pulled into informing our forward plan ahead,” she says.

Officials transitioned from emergency response to longer term plans at the end of September after fish began moving upstream toward spawning grounds naturally. While some narrow passages have been made, rock debris from the slide continues to create an “impassable” velocity of water and a height barrier for the fish.

At the same time that officials are preparing for lower water levels, they are making contingency plans and gathering ideas for longer term response strategies, Murdoch says.

But they are very much at the mercy of Mother Nature, she says, as water levels will play a big role in their success.

“This is a major remediation project and we only have the chance to do it once,” Murdoch says. “There is a high risk we will not be fully successful.”

The populations most affected by the slide have been early Stuart sockeye, two groups of spring and salmon chinook and the Interior Fraser coho population, she says.

More than 275,000 salmon managed to get past the slide. Of those, about 245,000 passed through naturally, while others were transported by helicopter and other means. Estimates on the mortality rates of those that were transported by helicopter were not available.

In September, the federal department adjusted the number of returning Fraser River sockeye expected this year to a little more than 600,000, down from an earlier projection of nearly five million.

An emergency measure to transport some of the Stuart sockeye to a hatchery at Cultus Lake is proving promising, and all 28,000 eggs hatched seem to be doing well, says Murdoch. Similar measures could be taken next season.

Officials are trying to be pragmatic and are preparing for the possibility of a long-term response.

“We may be at this for a couple of winters,” she says.

This report by The Canadian Press was first published Dec. 4, 2019.