As far as a dam, we don't have one. One side drops off slowly and I do worry about the roots of a willow on that side a bit. The vast bulk of the trees are on the inlet, or high side.
As far as dealing with excessive cattails, we would use a weed razor and call a work party. Cut them, pull out the cuttings and bag them for my garden.
We don't have near the shallows seen here, Our sides drop off pretty fast
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=373232#Post373232One question, Does the Sonar AS kill those trees on a single use or over multiple years?