How big is your infestation (around the whole pond or part? 6' out from the shore or more or less? How many years of growth?

IME with this plant; If the infestation is less than say 5 years old, chemicals would probably work just fine. You would have to stay on them a couple of seasons with herbicide to completly eradicate. Also mechanical removal by hand, once dead, would be manageable. As mentioned above, the plant needs to be actively growing for the gly to work.

If they are well established and you have the means, mechanical removal with equipment would solve your problem quickley. You would still most likely need to chemical treat new growth a few seasons after.