Both ponds are roughly 500 sq. ft. in area and apprx 4 feet deep in the middle. They are spring-fed from a source only 100 yards up the hillside in the Crystal Springs neighborhood of Bainbridge Island. The Crystal Springs area of Bainbridge is directly across the sound from Illahe State Park.
I do not believe I will become involved in the Koi fish business as the in-flow water is only 45 degrees and the lower pond outflow is only 48-9 degrees in August of 2008. Maybe a tad warmer water in a warmer summer, but not by much. Frogs don't seem to mind the cold water and Mallard ducks raise multiple clutches in the spring.
I believe that the most likely water plants will be varieties of Iris. I'm open to experimentation with Lilies and any suggestions from more experienced pond gardeners.
The ponds are "natural", excavated out of the clay / peat swamp in my back yard, no pond liners.
I constructed them with 6" PVC sewer pipe connecting the two ponds. The same size pipe provides the outflow of the lower pond to the existing stream. I am in the process of constructing surface "cascades" connecting the two ponds and the outflow of the lower pond.
The sewer pipe and valving system will remain in place for occasional work requiring temporary lower water levels.