@NinaSilver: I believe it's following the Northern Border Pipeline. They're crossing the river in virtually the same spot. In which case, they're protesting putting a pipeline where one already exists. I'm not saying it's right or wrong either way, but it seems weird to protest the pipeline if there's already one there.

@NoOneYouKnow: I found a thing + an external link on United States v. Sioux Nation of Indians

https://www.reddit.com/r/NoDAPL/comments/5fcoqe/who_actually_owns_the_land_where_the/

https://en.wikipedia.org/wiki/United_States_v._Sioux_Nation_of_Indians

If you can afford it, their website includes a donation link.

Thankyou.