ncharlie: I don't have a filter as it is a small pond and is very easy to just do water changes. I'd scoop out the water and use it to water my potted plants.
vicky: I have no problems keeping the lilies underwater over winter. The winter temperature in my area is 33-43F. When temperature does fall below freezing, the ice layer is usually thin so the rhizome below the ice doesn't freeze and the plant can stay dormant. The lilies and parrot feather are hardy to zone 3 (-40 to -30 F) and papyrus is hardy to zone 8. This is the first time I've kept those marginal plants in the photo. Id probably take the marginal plants above ground for the winter although they are supposed to also survive in the water under the ice as long as the roots don't freeze.