Thanks for the info.
I have tried to establish other marginal plants, but most don’t do well with my fluctuations in water level, losing 2ft most summers. The cattails put up with it just fine, and lilies are out further and don’t care. But marginals mostly dry up and die. Otherwise I certainly would!
Blue flag iris does survive, but it doesn’t do well in my poor clay soil. It also prefers to be right at the highest waterline. Yellow is darned aggressive and near impossible to pull out by hand, I have a bunch of them that need constant control and removal of seed pods. Again, at the waterline. So I am stuck with cattails.
I could probably kill some off, and plant some other stuff in their compost at this point. I have a feeling though that my level fluctuations will prevent success.
Meanwhile, my garden pond is overrun with desired plants. I certainly have a source!