Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
That does sound like it. Is it in large enough areas that you can get hold of it?
It will be slimy, and be easy to pull up, but falls apart. No internal structure. No stems, no roots. It usually smells bad (there are different species, some smell worse than others).
Most kinds look fairly dark under water, but usually some shade of blue-green. Removed from water they can look almost black.