BISMARCK, N.D. (AP) — Cleanup of a North Dakota encampment where opponents of the Dakota Access oil pipeline stayed for months to protest the $3.8 billion project is expected to take weeks, a leader of the tribe that organized the protest said Tuesday.

The Standing Rock Sioux hopes to complete the work before any spring floodwaters from the Cannonball River can wash debris into the Missouri River — the very waterway pipeline opponents are working to protect. The camp has seen an exodus in recent weeks due to winter weather, pipeline work being stalled and the tribe's recent call for people to leave.

Protesters have left behind not just trash, but tents and even cars.

"There's more than anticipated, and it's under a lot of snow," Tribal Chairman Dave Archambault said. "I wouldn't say it's going to get done in days; it's going to take weeks."

The camp is close to where the Cannonball River flows into the Missouri, a water source for millions of people, including the tribe. Hundreds and sometimes thousands of people have camped there since August to protest a pipeline that they worry will threaten drinking water and Native American cultural sites.

The four-state, 1,200-mile pipeline would skirt the tribe's reservation as it carries North Dakota oil through the Dakotas and Iowa to a shipping point in Illinois. Texas-based developer Energy Transfer Partners says the pipeline is safe.

Standing Rock's environmental protection agency organized the camp cleanup with the help of the Thunder Valley Community Development Corp. from South Dakota's Pine Ridge Reservation, which has arranged for heavy equipment including front-end loaders, dump trucks and skid-steer loaders.

"We'll be here eight to 10 hours a day all week. Then we'll reassess the situation," returning next week if necessary, said Nick Tilsen, Thunder Valley's executive director.

People who still have not left the camp are helping, bringing the total on the job to about 100, said Tilsen, who is among the workers. Cost of the cleanup isn't yet known, but the tribe will use money from the $6 million in donations it has received to support its pipeline fight, Archambault said.

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The tribe hasn't asked for help from the state or Morton County.

Republican Gov. Doug Burgum, who has traveled to the Standing Rock Sioux Reservation twice in the past week to be briefed about the situation, issued a statement saying the cleanup is "an important step toward addressing the safety and environmental risks posed by imminent flooding."

Minor flooding of the Cannonball River is almost certain this spring in the camp area, according to the National Weather Service's first flood outlook of the season, issued Friday. The next outlook, on Feb. 16, is expected to provide a clearer picture of potential flooding.

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