If it were mine, and the funds were available, I'd dig out the old pipe, remove the trees (and roots) from the dam, and see about making the pond deeper (removing the organic sediment that has built up in the pond basin at the same time), and go with a siphon system. Drawing the water from the lowest portion of the pond.

My concerns with just plugging the pipe is that one of the trees could die (or already has) and the decomposing roots would compromise the dam. I'd hate to get the pond just the way I envisioned it and have the dam start leaking.


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