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More than 80 people protesting a controversial North Dakota oil pipeline project were arrested Saturday and pepper spray was used in what the sheriff’s department called a "riot."

Saturday’s arrests occurred in a confrontation with police after around 300 demonstrators trespassed on private property along the Dakota Access Pipeline project's right of way, the Morton County Sheriff's Office said.

Protests have been held for more than two months against the project, which the Standing Rock Sioux Tribe says the pipeline project would destroy some of its sacred sites.

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This photo provided by the Morton County Sheriff's Department shows some protesters and police during a demonstration against the Dakota Access pipeline project in Morton County, North Dakota, on Saturday, Oct. 22, 2016. Morton County Sheriff's Department

The confrontation between police and protesters began at 5:20 a.m. Saturday and lasted five hours, according to the sheriff’s office spokesman Rob Keller. Protesters have camped for weeks about five miles from the site, close to where the Missouri and Cannonball rivers meet.

The sheriff department’s statement said law enforcement officers decided to use pepper spray when protesters tried to breach the line they had created between the demonstration and construction equipment. It added that a protester disarmed an officer and used his own pepper spray against him, blinding him for up to five minutes.

Morton County Sheriff Kyle Kirchmeier said Saturday's confrontation shows "that this protest is not peaceful or lawful."

A section of a state highway had to be shut down because of the protests, but has since reopened.

"It was obvious to our officers who responded that the protesters engaged in escalated unlawful tactics and behavior during this event," Kirchmeier said in a statement. "This protest was intentionally coordinated and planned by agitators with the specific intent to engage in illegal activities."

Eight-three people were arrested in all, the sheriff's office said.

Four of those arrested Saturday had attempted to attach themselves to a sports utility vehicle parked on private property close to the construction equipment. Two fastened themselves to the exterior of the car, one bound himself to the steering wheel, and another fed his arm through a hole in the door and had his hand stuck inside a bucket of hardened concrete.

In this photo distributed by the Morton County Sheriff's Department, a Dakota Access Pipeline protester fastens himself to a car with his hand stuck in a bucket of hardened concrete on the other side. Morton County Sheriff's Department

Charges of those arrested include assault on a peace officer, criminal trespass and engaging in a riot.

Texas-based Energy Transfer Partners were granted approval for the 1,172-mile, 30-inch diameter pipeline earlier this year. The project runs from Illinois to North Dakota, cost nearly $3.8 billion and could move up to 570,000 barrels of oil per day once completed.

Protesters, many of whom are members of the Standing Rock Sioux Tribe, are worried about the potential environmental impact to the Missouri River and the possible desecration of nearby sacred sites. Plans are to cross under the riverbed less than a mile from the tribe’s reservation.