The clashes began after protesters removed a truck that had been on the bridge since Oct. 27, police said. The North Dakota Department of Transportation closed the Backwater Bridge due to damage from that incident.
The $3.7 billion Dakota Access project has been drawing steady opposition from Native American and environmental activists since the summer.
Completion of the pipeline, set to run 1,172 miles (1,185 km) from North Dakota to Illinois, was delayed in September so federal authorities could re-examine permits required by the Army Corps of Engineers.
Plans called for the pipeline to pass under Lake Oahe, a federally owned water source, and to skirt the Standing Rock Sioux Reservation by about half a mile. Most of the construction has otherwise been finished.