It's a major priority for the NYPA (Canal Corp) to remove trees from their dams, because they are dangerous, and likely to cause a flood if the dam collapses. There is also the threat of old trees, especially Cottonwoods, dropping limbs on passers by on the towpaths. This is why the EEIP (SEQR) has now widened its scope to about 100 feet either side of the canal for it's entire length, and whether there is a dam, or not. (Thank the Stop The Clear Cut group for this new development!)
That means if your property is adjacent to the canal, and the trees overhang the water, or pose a threat in any way, the NYPA will likely cut them down. Why?
Because they could fall on a passing boat, kayak, or NYPA worker. The NYPA is liable, after all, they own the trees. They have the right to come onto your land, to get to their shoreline and do whatever they like.
Get used to it!