I am trying to visualize this in my head. If he had room in the back of the dam, why couldn't he just add a few feet of clay to the rear? You would still have to fix the tree situation, but the original dam should be holding the bulk of the pressure. This would be just a long term patch job. I imagine the cost would be much cheaper, and the fish would be fine.
How bad is the damage to the dam from the trees? How big of roots are into the dam? If he stopped the water flow through the dam and sealed it with new clay. Wouldn't the dam seal itself as the roots decomposed?
