About 200 people protesting the Dakota Access pipeline are facing off with law enforcement near the mouth of the Cannonball River.
Officials say protesters were trying on Wednesday to get onto private property owned by the pipeline developer.
About 30 people are in waist-deep water confronting law enforcement officers, while others are on the banks.
Medics were treating some protesters for hypothermia and others who were hit with pepper spray.
Morton County sheriff’s spokeswoman Donnell Hushka says some protesters tried to build a wooden pedestrian bridge across Cantapeta Creek, which runs near the private property.
The permanent bridge at the site has been shut down since it was blocked last week by burned vehicles.
Huskha says officers used a boat to pull apart the makeshift bridge.
President Barack Obama says the U.S. Army Corps of Engineers is examining whether the Dakota Access oil pipeline can be rerouted in southern North Dakota to alleviate the concerns of American Indians.
Obama says his administration is monitoring the situation closely but will “let it play out for several more weeks.”
The Standing Rock Sioux tribe worries that the $3.8 billion pipeline from North Dakota to Illinois will threaten its drinking water and destroy sacred sites.
Protests that have included clashes with police have gone on for several months in North Dakota.
Obama calls it “a challenging situation.”
He says there’s an obligation for protesters to be peaceful and for authorities to show restraint.
The 1,200-mile pipeline is largely complete outside of North Dakota.