Sorry I can't supply any pictures, but can anybody identify the creatures living on my pond waterfall? I built it myself with huge rocks, and the pond has been established for about five years. There are small black worms about 6-8mm long in layers about 2mm thick in all the parts of the waterfall that are constantly wet, but not directly under the strongest part of the flow. They are also in the waterfall outlet pipe.
For want of a pondy keeper round here, 2010 is your man really, but he isn't on here all nights, I'd think it would be a kind of blackfly larvae ('simulium' perhaps) common and as far as I know causes no danger to fish as such.
Take a reccy on google images in the interim so get an ID