my room mates duck devoured all my parrots feather over night....

Link to various plants listed as food for waterfowl (ducks)

Wild Celery
Arrowhead (Duck Potato)
Arrow Arum
Pickerel Weed
Burr Rush

Ducks will eat small fish, submerged and other plants, corn, acorns, grains of various types.

Here is a link that might be useful: Water Plants for Wildlife

Ducks like to eat grass; regular lawn grass is fine. They'll graze on it like geese.

It's really hard to keep a pond vegetated with ducks around. They'll clean out any edible aquatic plants in short order (at least, the mallard-descended domestic ducks will).

I'm not sure whether muscovy ducks will graze on aquatic plants to the extent that the mallard-types will.

Or are these wild species of ducks? If so, there are some that are mostly or exclusively carnivorous (mergansers, goldeneyes, etc.).

Ya, although it sounds like a great idea, a few duck can easily take out all your plants in a short while. Their diet would have to be substituted with grains and such, otherwise your going to be throwing in more plants into that pond than you can handle. The thing with most aquatic plants is that unless you give the pond a few years to let the plants grow, they are going to be far and wide if you throw some dabbling species of ducks in there. If your client doesnt intend on eating these ducks or hand feeding them bread and such, get some diving ducks and stock the pond with fish.

Also another plant not mentioned was wild rice. Other than the plants mentioned, your really getting yourself into a big project. I would talk to an expert on ducks, or try to find an ecologist.

There are sites on managing land and water for ducks. Look up duck hunting.

Hi
There is a site called "Gamebirds and Waterfowl' That will tell you everything you ever wanted to know about them.
Designing a pool for them requires some careful planning as to size depth and so on.. Waterfowl are very messy . lol
gary

I know this is an old question, but I thought I'd throw in my two cents:

We have a Pekin duck and she loves to eat grass and clover. We've been talking about putting in a pond for her and adding some duckweed. Ducks eat a lot of veggies and duckweed is an invasive pond plant...we're hoping that the two will cancel each other out.

Of course our duck gets her usual feed as well. The veggies are more of a treat for her. With the right balance, I'm hoping that the duckweed will grow fast enough that she won't be able to eat ALL of it. But if necessary, I'll cage off a small section of the pond where the duckweed can grow without the duck reaching it so she CAN'T eat all of it!