HELENA, Mont. (AP) " A federal judge in Montana on Wednesday lifted his hold on a proposed irrigation dam and fish passage that U.S. officials say is the best hope to save an endangered ancient species of fish in the Yellowstone River.

U.S. District Judge Brian Morris allowed the U.S. Army Corps of Engineers and Bureau of Reclamation to proceed with the $59 million project over arguments from wildlife and conservation groups that the new construction could make matters worse for the survival of the river's remaining pallid sturgeon.

"We feel that this approach is the best one for everyone affected, including the pallid sturgeon," Corps of Engineers spokeswoman Jamie Danesi said.

The Corps of Engineers issued a notice to its contractor to proceed with the project, though it will likely be months before construction begins, and two to three years for it to be completed, Danesi said.

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A spokesman for a wildlife advocacy group that sued to stop the project said he doesn't believe the fish will use the bypass channel, and that his organization will continue to press for removing the dam altogether.

"We're disappointed in the judge's decision to lift the injunction, but we're going to continue to fight for pallid sturgeon and work for an open-river solution in the future," Defenders of Wildlife spokesman Aaron Hall said.

There are about 125 of the long-snouted fish in the Yellowstone, making it the largest existing population in the wild. The fish can grow up to 6 feet long and have been around since the time of dinosaurs, though their survival is in jeopardy because they haven't been able to swim downstream to their spawning grounds for decades.

An existing rock weir that diverts river water to an irrigation system for about 400 eastern Montana farms blocks the pallid sturgeons' passage. Defenders of Wildlife and Natural Resources Defense Council sued the federal agencies in 2015 to remove the weir, leading the agencies to propose building a new dam and a bypass channel for the fish.

The judge issued an order blocking that plan in November 2015, saying the agencies' environmental review didn't study whether the pallid sturgeon would be likely to use the new channel, and he ordered U.S. officials to conduct a more thorough analysis.

Attorneys for the U.S. Department of Justice asked the judge earlier this year to lift the injunction after that analysis was completed in 2016.

The wildlife and conservation groups contended that the new environmental analysis didn't actually answer the question of whether the pallid sturgeon would use the new bypass.

In Wednesday's ruling, Morris wrote that he lifted the injunction because the Corps and the Bureau of Reclamation's new environmental review "attempted to address adequately pallid sturgeon recovery and probability of success of the bypass channel."

The judge's was applauded by the irrigators who use the existing century-old rock weir that the dam will replace.

"The judge removing the injunction is a huge victory for the pallid sturgeon," said James Brower, the project manager for the Lower Yellowstone Irrigation Project. "If the injunction had stayed in place any longer, the fish would have become too old to reproduce and the species would have died out."

However, the judge also allowed Defenders of Wildlife and Natural Resources Defense Council to update their lawsuit to challenge the new environmental review. Hall said they plan to do so and seek another injunction before the dam is completed.