What’s THIS?

[RedSetter]

Hello all. This substance is clinging to a once very healthy Elgeria in my tiny pond (at least, I think that is the plants name)
Does anyone know what it is and if it’s a good or bad (or neither) thing? The plant isn’t looking too healthy
Thanks
Red

 

[Fishfur]

What happens if you shake the stems? It looks rather like accumulated debris but it has tiny, umm, well, let’s call them hairs for now, as I don’t know precisely what they are.