Look at the photo above carefully....study it...and think about what you are seeing.
It is probably not what you think it is. It is not a chemical spill, run-off from some mud-slide, run-off from a heavy rain somewhere up stream.
This is actually two streams meeting. One, the clearer one, is a river formed from snow melt that began high on an Alaskan mountain and raced down the side of the mountain past Dahl goats and big-horn sheep and down past black spruce allowing them to drink before racing on into the ferns of the boreal forest. Then it trips over smooth boulders and reaches the flat lands where it joins the other river.
The other river races from beneath a melting ice glacier and does not fall so far nor have time to drop its fine silt, the silt is granite that has been ground into a powder so fine you cannot hold it, so fine when it settles on the river floor you can drown in it. It can grasp your leg like wet cement and will not let go.
In the photo above I was fascinated by this meeting of the waters. (As always you can click on the photo for a closer look.)