Be careful here... a lot (most) of the traditional fish pond, water garden, and bog plants are toxic to ducks. Cannas are safe, but get large and invasive. Be sure and check everything. Even stuff that seems benign -- like rushes -- are poisonous. I had a hell of a time landscaping our pond as there is no good resource. A UK guide to keeping waterfowl I read even lists Rhodedendron as a good plant for duck enclosures... horribly toxic! Make sure you confirm toxicity with at least two sources. I poisoned one of my ducks by letting her forage under a beautiful and evil tree... and have to live with that. Ripped it out with my bare hands.