How much shade is too much?

A friend has invited me to help her "do something" with a big back yard that was largely grown wild when she and her housemates moved in.

One of their discoveries when they cut back the underbrush was a small pond built underneath one of the giant tree-shrubs surrounding the yard. The pond is completely overhung by thick-leaved branches, so gets very very little light.

Are there plants that would thrive in such an environment, or do we need to cut back some of the overhang?

think of the Amazon jungle. total shade, and plants EVERYWHERE.

well since you're in the Seattle area, aren't there a lot of indigenous ferns that do well in the shade?

Can the overhanging branches be thinned and cut back?

Hellebores and astilbes will grow in the dark. Also hakone grass, farfugium, ligularia, epimedium, many ferns, camellias, violets, mondo grass. The shade will slow the growth of everything down though. Sword fern will almost grow anywhere. You may have more trouble with root competition if there are large shrubs overhanging the planting area.

cat palms!