As we start to enter fall here in the northern regions, pond plants are the first indicators that the pond season is coming to a close. I have to admit, my potted pond plants did very well this year. I think there were two reasons: one, we had lots of good weather, healthy rains, moderate temperatures and plenty of sunshine; and second, I took the time in early spring to divide the root-bound plants and add new soil. I have several potted lizard's tails and elephant ears that went absolutely crazy.
Now is the time to cut away all dead growth and trim back the live to a few inches above the pot. Irises, lilies, umbrella plants, lotus, all marginals and deep water plants should be submerged to prevent freezing over winter. If you have a bog, trim back the plants and cover with mulch. As far as floating plants go, you can bring them indoors and keep them in a cool, dark, temperature-stable environment. I generally treat them as annuals and buy new plants in the spring. Last year, we brought the elephant ears and calla lilies inside to our sunroom, and they did quite well. It allowed us to enjoy the plants all year long.
A funny story: I lost most of the water hyacinth I had purchased earlier this spring, thanks to my over-active Koi batting them around and nibbling at the roots. However, my wife had an idea. She purchased a rubber, floating dart with a bright orange tail at the grocery store and tossed it into the pond. Sure enough, the Koi have spent hours batting that around and have left the one poor, disheveled hyacinth alone. We'll see next year if it really works.