This junk is attached to the rocks in certain sections of the river. It grows in areas conducive to algae, shallow areas where sunlight can get to the bottom easily and where the current isn't too fast. The further you go upriver the more shaded the water gets with the higher bluffs. If it was the hatchery, what would they be releasing that looks like algae and cotonwood seed? Why would it be attaching itself to rocks downriver as far as Castle Rock? If they were somehow dumping this crap in the water, would they really have enough material to keep it flowing in the river all the way into August? It seems like it would flush out in a couple weeks if it was only coming from one point in the river. Has anyone bothered to call the hatchery and ask them about it? Whatever it is, it's organic and isn't toxic, it just is a pain in the butt.