The federal government announced Friday it was dispatching Bureau of Indian Affairs agents to help clear Dakota Access Pipeline protesters from the Standing Rock Sioux reservation.
The tribe has been lobbying against federal approval of the 1,170-mile pipeline, which crosses four states and would carry crude oil from the rich shale oil basins of western North Dakota to the pipeline networks and refineries in Illinois.
While many business, farm and labor organizations back the project, arguing it remains the safest ways to transport oil, a coalition of tribal and environmental groups argue it will accelerate climate change and could disturb sacred burial grounds and archaeological sites.
In response to a directive from President Donald Trump, this week the acting secretary of the Army, Robert Speer, has ordered the Army Corps of Engineers to expedite review of an easement for the pipeline to run under Lake Oahe.
But some protesters have remained on site, even as weather conditions have deteriorated and tribal officials have said they will fight any federal permit in court. Corps officials have said that the extended protests have contributed to soil erosion that could make any potential flooding worse.
Some activists have moved to higher ground, and on Wednesday authorities arrested 74 of them who had decamped to land owned by the pipeline's developer, Energy Transfer Partners.
Acting assistant secretary of Indian affairs Michael S. Black said the agency had sent "enforcement support and will assist" the tribe "in closing the protest camps within the Standing Rock Reservation boundary."
"North Dakota Governor [Doug] Burgum, the Standing Rock Sioux Tribe leadership, local law enforcement, and local landowners have all warned the public and those still camped of the dangerous spring flooding expected due to the heavy amount of snowfall the state received this winter," Black added. "The closing of the camps is a matter of public health and safety and working together at this time will allow for the safe removal of waste and debris that will impact the local environment and protection of those camped."
The Standing Rock Sioux Tribe had already passed a tribal resolution asking protesters to leave, and asking for federal aid in closing the camp.
"In these past few weeks at camp, I see no reflection of our earlier unity, and without unity we lose," the tribe's chairman, David Archambault II, said in a statement.