As cold weather approaches, trim hardy lotus and lilies and then put them in the deepest part of the pond. Other hardy plants such as grasses, cattails, and iris do not need to be trimmed back in temperate zone gardens, but for colder climates just put them at the bottom of the pond for the fish to hunker down in.
You can also remove and/or compost tropical oxygenators and floating plants like water lettuce and water hyacinths. If you have space, you can bring your plants inside. Some of the ones that are a little more fragile you can put into plastic tubs and overwinter indoors. Remember to provide them with light, keep them damp and check on them weekly.