Question
we have a country pond about an acre in size, which is being overgrown by lilypads & cattails. Is there any pond treatment that would not be toxic to the fish or to swimmers?

Answer
I am against herbicides.  None are truly safe.  Some will probably be ok for fish and humans to some extent.  Not using them myself, I don't have a preferred toxin.  Cattails can be almost impossible to get rid of even with toxic chemicals.  Lilies are eaten by many animals - koi, grass carp, turtles, muskrats, beavers, deer, raccoons, ducks, etc.  Physical removal might be doable for the lilies but cattails are hard to pull or cut.  I suggest contacting some of the companies that cater to farm ponds.  They sell machinery and chemicals to kill plants.  I have a list at http://www.fishpondinfo.com/farm.htm

Good luck!
Robyn