Doesn't like Kool-Aid
Join Date: Feb 2003
Location: Hawthorne, New Jersey
Have you added the plant recently, or did healthy plants go bad?
If it is a newer plant, the odds are that the plant was grown emmersed (out of water) and is in the process of adapting to life underwater.
Leave the plant there, clip off the brown stuff and wait a bit. I think new, submerged growth will appear in no time.