Linda Black Elk, a member of the Standing Rock Medic and Healer Council of the Catawba tribe, said..."Last night was a really critical life or death situation"... Standing Rock Sioux Chairman Dave Archambault II told NBC News that between 200-300 people were transported late Sunday night to a gymnasium on the Standing Rock Sioux reservation for treatment for hypothermia, facial and hand wounds, and other minor injuries... 

Protestors say that the clashes began when they tried to remove a roadblock on a bridge north of their Oceti Sakowin "Water Protector" Camp. The roadblock...has blocked the main route to the city of Bismarck since late October. "The negotiation from law enforcement stated that they were going to remove them for their emergency services to get through ... to Bismarck. It's been 2.5 weeks, maybe 3, and they still haven't kept their word on that," said E'sha Hoferer... Black Elk said the roadblock was an inconvenience and posed a risk for emergency personnel trying to access the protest camp...

Sheriff's spokesman Rob Keller told NBC News that...water was sprayed from a fire truck to control fires as they were being set by activists. However, video posted to Facebook by activists clearly showed authorities spray a continuous stream of water over demonstrators in areas where there were no fires...

[The] Standing Rock Sioux Tribe argues that the proposed pipeline could permanently contaminate its water source, the Missouri River, as well as desecrate sacred sites. Energy Transfer Partners, which is behind the pipeline, has said that it has taken measures to prevent such leaks and that the pipeline is far safer than transporting oil with trucks or trains. 

[Video of police response to protesters]