A celebration erupted at the main protest camp in Cannon Ball, North Dakota, where the Standing Rock Sioux tribe and others have been protesting against the 1,172-mile (1,885-km) Dakota Access Pipeline.

It may prove to be a short-lived victory, however, because Republican President-elect Donald Trump has said he supports the project. Trump takes over from Democratic President Barack Obama on Jan. 20 and policy experts believe he could reverse the decision if he wanted to.

The line, owned by Texas-based Energy Transfer Partners LP, had been complete except for a segment planned to run under Lake Oahe, a reservoir formed by a dam on the Missouri River.

That stretch required an easement from federal authorities. The Obama administration delayed a decision on the permit twice in an effort to consult further with the tribe.

“The Army will not grant an easement to cross Lake Oahe at the proposed location based on the current record,” a statement from the U.S. Army said.

Jo-Ellen Darcy, the Army’s Assistant Secretary for Civil Works, said in a statement the decision was based on a need to explore alternate routes for the pipeline, although it remained unclear what those alternatives would be.

Energy Transfer Partners and its partner Sunoco Logistics blasted the decision in a statement, calling it the “latest in a series of overt and transparent political actions” by the Obama administration. They said they were committed to seeing the project completed without rerouting the line.

Protesters have said the $3.8 billion project could contaminate the water supply and damage sacred tribal lands.

“I hope they follow through here with this. They haven’t been following the law all along. So we’ll see – but this is a victory today for our people and our water,” said Native American Gerad Kipp, 44, an irrigation engineer from Missoula, Montana.

Standing Rock Chairman Dave Archambault II thanked activists for their support in the protest effort.

“The Standing Rock Sioux Tribe and all of Indian Country will be forever grateful to the Obama Administration for this historic decision,” he said in a statement.

“We want to thank everyone who played a role in advocating for this cause. We thank the tribal youth who initiated this movement,” he said.

Protest organizers had for months argued that crossing the Missouri River adjacent to the Standing Rock Sioux Reservation presented a danger to their water source.

Protests grew over the months, with hundreds of veterans flocking to the camp in recent days to stand against what they said were aggressive law enforcement tactics.

Activists at the camp were seen hugging each other and letting out Native American war cries on Sunday, but many remained wary, knowing that Trump has voiced support for the line.

“It’s not a 100% victory. But I think the people who’ve been here for almost eight months have earned the right to be excited today,” said Eryn Wise, 26, an organizer with International Indigenous Youth Council.

‘FAILS TO RESOLVE ISSUE’

North Dakota Congressman Kevin Cramer and Senator John Hoeven, both Republicans who favor the line, blasted the decision, saying it “violates the rule of law and fails to resolve the issue.” Cramer, an adviser to Trump under consideration for a Cabinet post, said the president-elect would “restore law and order.”

Trump has yet to react to Sunday’s decision.

“He could approve the pipeline within a matter of hours of taking office,” said Brigham McCown, the former head of the U.S. Pipeline and Hazardous Materials Safety Administration under George W. Bush. “He can simply reinstate the previous decision or by executive order say that it’s part of national critical infrastructure and approve a permit.”

Still, the pipeline route’s opponents said they hoped the line would be rerouted.

“We’re hopeful that when the Trump administration takes office it will look at all of the priorities it has and that putting at risk the water supply of the Standing Rock Sioux isn’t on their list,” said Michael Brune, executive director of the Sierra Club.

Any alternative route would still likely need to cross the Missouri River, probably upstream of Lake Oahe and closer to the state capital of Bismarck. Many pipelines travel under U.S. waterways already, and pipe is considered a safer way to transport crude oil than rail.

North Dakota Senator Heidi Heitkamp, a Democrat, acknowledged that the next steps remain unclear, saying in a statement Sunday the pipeline “still remains in limbo.”

Pipeline proponents are looking to different policies from the incoming Trump administration, particularly after the Obama administration’s denial of the Keystone XL pipeline, which would have come from Canada through Nebraska. A number of states and municipalities have made it more difficult to build pipelines in recent years.

“With the federal environmental assessment finding the current route will have the least impact on the environment, we’re looking forward to getting past this administration’s politicization of Dakota Access and future decisions made on the merits of this project,” said John Stoody, a spokesman for the Association of Oil Pipe Lines, in Washington.