Hubbard County Sheriff Cory Aukes said the incident began about 7:30 a.m. Tuesday when a van pulled in front of the semitrailer and forced it to stop on a county highway. Several carloads of protesters soon arrived.

Aukes says deputies began arresting demonstrators after they began “yelling vulgarities, being a traffic hazard, and refusing to leave.” At least 1,000 activists from across the country gathered at construction sites near the headwaters of the Mississippi River last week.