I'm trying to ID a plant (I'm assuming it's a weed) that I see when out driving on the highways in Saskatchewan and Alberta. I'm near Saskatoon.

It grows mostly at the edges of sloughs. It's taller than the surrounding plants and reddish....sort of a browny red.

I've searched prairie weeds, added the word slough...various types of searches and I can't even find a photo of the darn thing.

I know this is fairly vague, but any help would be appreciated.