"Law enforcement is currently engaged in a standoff with protesters on the banks of the Cantapeta Creek," said a news release from the Morton County Sheriff's Department. "Protesters are trying to gain access onto private property also known as the Cannon Ball Ranch."
Police saw protesters building "a handmade, wooden pedestrian bridge" early Wednesday morning, police said.
The US Army Corps of Engineers ordered the Morton County Sheriff's Department to remove the makeshift bridge and arrest protesters trying to cross it with criminal trespass.
"Officers responded and ordered protesters to remove themselves from the bridge and notified them that if they cross the bridge they would be arrested," the news release said.
Once police pulled the bridge apart with a boat, protesters swam and used their own boats to cross the river, police said.
Protesters are being warned that anyone crossing the river to enter private or Corps of Engineers property will be arrested and could be charged with violating numerous federal and state laws.
According to the North Dakota Cowboy Hall of Fame
, the 7,500-acre ranch is at the confluence of the Cannonball and Missouri rivers, just north of the town of Cannon Ball and about 40 miles south of Bismarck.
Cannon Ball Ranch is one of the state's oldest, serving as a gathering point as early as 1865. Later, in addition to accommodating cattle, mules, sheep and hogs, it also hosted a hotel, a general store, ferry crossing, steamboat landing, telegraph station and stage line over the years.
Media reports indicate
that Dakota Access LLC, the company building the pipeline that has sparked the protests, bought 6,000 acres of the ranch in September.
The Corps of Engineers OK'd the $3.7 billion project in July, setting off the showdown that continues today.
On one side are proponents who say the 1,172-mile pipeline will transport valuable oil out of the Bakken Formation, a vast underground deposit where Montana and North Dakota meet Canada. There's an estimated 7.4 billion barrels of oil on the US side of the formation, according to the US Geological Survey.
On the other side are members of the Standing Rock Sioux Tribe, which is suing the Corps and says the pipeline will "destroy our burial sites, prayer sites and culturally significant artifacts." They're joined by environmental activists who worry about possible water pollution and greenhouse gas emissions.
President Barack Obama entered the fray on Tuesday
, saying that his administration is devising options to reroute the pipeline.