Sorry fellas.......it is indeed fillamentous algae as Salmo mentions. we have the same crap here on the Wynoochee every June/mid-July. It seems to be worse the past decade locally. Warm-water, above average sunny days(mild spring) and high nutrient loads all contribute. The algae's life cycle seems to endure 2-3 months before dying off. Some years it appears mid-June; other years, like this year, it started showing in early may......again, locally. I attribute it to our warm, mild spring.

I count the days waiting for the stuff to die off (and it will) so I can drift a bait without reeling in a foot of "snot" attached to my rig.......probably a good time frame to go bobber and jig.

You guys all mention cottonwoods but I can't help but wonder if it's as simple as cow poop in unchecked/unfenced riverside pastures contributing to a high nutrient load?

Whatever the case, it is indeed a pain in the arse.