The police are meant to be a peacekeeping force, and that's exactly what they should be doing.
The people at Standing Rock are protesting peacefully. They're not hurting or disrupting anyone or anything.
I think it's ridiculous that in a country supposedly built on free speech and liberty, the government/police are allowed to suppress these protests so brutally. Tear gas and high powered water guns for harmless, unarmed men and women? Pathetic.