uh-oh...lemons, lemons...what am I gonna do with lemons? I know!
C'mon, now. You musta known that you were gonna need/want a small wetland area for birds and spawning...right? Those trees won't be long for greenery, but sure will look good to the fish and wildlife.
If the dam is holding well after all is said and done, it would be a tuff decision to try to lower the principal to allow the island to re-emerge....adding makes more sense to me. Quite frankly, there is a good chance that those trees weren't gonna last real long anyway with the soil saturated at a depth 24" below grade. You are gonna look back at this and remember how good that lemonade really was.
Dude....you got yourself a pond!