As for the San juan worm, there are water born worms in most waters called oligacheats{sp?}. They live in the sediment and detritus of lotic waters. They don't really appear to be much different morphologically than a tiny earth worm.
I used to do BMI surveys{benthic macro-invertebrate surveys}in the lackawanna, for the Lackawanna river corridor Assoc. when I was in highschool, from '90-'92. Large counts of these worms showed up from all sample sights, however the greatest portions of them showed up from areas being tested that had the greatest amount of siltation due to runoff.
To me, a san juan worm, is as valid as a crane fly larva, or stone fly nymph, etc.
Just a FYI, and many may know this, but the "San Juan shuffle" was a technique where by anglers would kick up sediment in the Rio Grande (I believe), by shuffling their feet, and un-earth these worms, then they would use this pattern dropped back in the "chum slick" if you will. Last I heard CO's watch for this as it has been deemed illigal in that river.
Tighlines