Need close up pics. A couple of guesses below.

Could be filamentous algae or Periphyton which is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems.

See this - https://forums.pondboss.com/ubbthre...s=Periphyton+&Search=true#Post574672

Last edited by ewest; 09/15/25 12:11 PM.