By Ernest Scheyder and Valerie Volcovici

CANNON BALL, N.D./WASHINGTON (Reuters) - The U.S. Army Corps of Engineers said on Sunday it turned down a permit for a controversial pipeline project running through North Dakota, in a victory for Native Americans and climate activists who have protested against the project for several months.

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

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, which 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 remains unclear what those alternatives will be.

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 Gerad Kipp, 44, an irrigation engineer from Missoula, Montana and a Native American.

In a statement, 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.

"We want to thank everyone who played a role in advocating for this cause. We thank the tribal youth who initiated this movement."

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 say are aggressive tactics from law enforcement.

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

"It's not a 100 percent 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, at the camp.

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."

Supporters of the line as well as opponents pointed out the Sunday decision does not resolve the issue.

It is unclear what the new pipeline route will be and any 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, nodded to the fact that the next steps remain unclear, saying in a statement Sunday the pipeline "still remains in limbo."

Energy Transfer has said in the past they did not intend to reroute the line. Even if the easement had been granted, it would have been months before the line was completed.

It is unclear whether Trump's incoming administration may consider taking up Energy Transfer's request yet again, and approving it. Trump's transition team last week said he was supportive of the line, in addition to other pipeline development.

"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

Pipeline proponents are also 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 down from Canada through Nebraska. A number of states and municipalities in the country 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.

A spokesperson for Energy Transfer Partners could not immediately be reached for comment.