At approximately 6:00 pm, protesters pulled one of the burned out trucks from the barricade area on the north side of the Backwater Bridge using a semi-tractor.  They failed to comply with law enforcement orders to leave the truck alone and to disperse.  Law enforcement formed a line at the barricade.  A group of protesters estimated at 400-500 person was eventually present on the bridge and in the immediate area.  They were failing to comply with law enforcement orders and were reported as throwing rocks, logs, and other materials at law enforcement officers on the line.Law enforcement utilized chemical agents, less-lethal munitions, and water sprayed from a fire truck to provide for protections and for crowd control and dispersing of the protesters.  The protesters started small fires in the area of the bridge to provide warming fires.  At least one explosion was heard in the area occupied by the protesters, possibly from an improvised explosive device of some type. Morton County TOC was informed the Standing Rock ambulance service was responding to the area of the Seven Councils Camp to provide medical services to protesters.   As of approximately 1:30 am, 1 male subject was arrested on an initial charge of Disorderly Conduct. A group of approximately 50-75 protesters remained on the bridge throughout the night.