I second what Greg said about Reward. I used a Reward/Cutrine mix to treat Elodea and it worked wonders. Not to contradict anything that Tea Lea says (he's an expert and I'm an amateur) but I would ONLY mechanically remove elodea that has been treated and is dead. One of the ways Elodea spreads is through plant fragments. I made the complete idiotic mistake of trying to manually remove live Elodea and the end result was that it spread all over the pond! I'd recommend that you treat a small section of the pond with Reward. My experience has been that with a Reward application you will see the plant dying back within a couple of days - it will turn brown and the leaves will shrivel. IMHO, I would wait for a couple of weeks to make sure that the plant is completely dead before you manually remove it. Reward will do the job, I can attest to that.
