(1) The water is pure and clear, like glass.
(2) There is no sediment, except after a storm, but then it clears out.
(3) The riverbed is all rock, Serpentine rock, and somehow this is one of the dynamics for the blueness.
(4) There is no moss because the river is swift and cold, although there can be some moss in summer in certain areas.
(5) The sky here, when clear, is incredibly blue, which is reflected by the water.
I found, by examining my photos, that the water reflects blue and green and turquoise at any angle, which must be from the rocks. Serpentine can look dull when dry, but get it wet and it has a whole new dynamic.
The amazingly beautiful Smith River:
At this angle, incredible turquoise is reflected
I turned and shot the other direction, and less blue is reflected
A very low angle, my camera was almost touching the water
Looking down, the rocks are grayish white when dry but lovely when wet
You can't deny the amazing dynamic of America's last Wild River, no dams!