Pat, here's just a few personal observations of PD (It's too long and hard to spell).
It's one of those plants that does have some advantages, and fry cover is one of the main ones. It comes up earlier than my A Pondweed, and provides cover earlier in the year. The only real problem with it, is the potential for uncontrolled spreading. After having initially found it 3 years ago, it now almost completely surrounds my big pond. I've also found it in an approximately 1 acre 3-4' flat that started getting popups all over it. That in and of itself isn't a bad thing, but once it's treated, it really doesn't die back. The dead plant just stays there, and gets algae covered. It reminds me of an upside down snow cone. Fishing becomes problematic at best, and that area was treated and drug primarily for recreational purposes.
I personally haven't seen it out compete any other shoreline plants like water primrose, lilies, reeds, or A Pondweed. It also seems to have less spread then they do, but it obviously can reestablish itself in deeper water if the clarity is there.
I'm not removing it because it does fill a niche, but I am keeping an eye on it.
