Tel,
What's up? It's Dave from the Bullocks.
I'd suggest going to Uajimaya in Seattle right now and picking up some fresh water chestnuts. They'll grow great here. For good instructions on how to grow them grab a copy of
Ecological Aquaculture.
Other good aquatics for this area include spatterdock (
http://www.pfaf.org/database/plants.php?Nuphar+polysepala), cattail, and lotus (
http://www.pfaf.org/database/plants.php?Nelumbo+nucifera).
Check those out and see what you come up with. Check out this nursery in Monroe to find a source for plants (
http://www.monroewatergardens.com/). Be warned, though. Aquatics are expensive! If you get them, I'd suggest propagating them and selling some to recoup your cost.
Hope all is going well for you!
Dave