BISMARCK, N.D. (AP) – Harsh wintry weather is forcing some protesters against the $3.8 billion Dakota Access pipeline to leave a vast camp in North Dakota.

The Morton County Sheriff’s Office estimates between 1,800 and 2,200 people remain at the camp on federal land. That’s down from the estimated 3,000 to 5,000 protesters before a couple of storms brought heavy snow and bitter-cold temperatures.

Tribal Chairman Dave Archambault has called for the camp to disband, though Native American rights activist Chase Iron Eyes has implored protesters to stay.

A coalition of grassroots groups opposing the pipeline issued a statement Friday saying they support a transition to protesting against project investors. But they say they also support pipeline opponents who choose to camp overwinter.