It could be as Shorty suggests some form of filamentous algae growing on stems of a plant like Eleochris. Do you have other similar bare stem plants in the pond that don't have the hairs??. Filamentous algae can grow very strongly attached to substrates. IMO the only way to know for sure is to look at some of the hairs using a microscope at 100X-400X and see if the hairs have the structure of FA or not. FA filaments will have unique cell structure.
