Some info.. not sure about the trees being IN the water but, this might help.
http://www.des.state.nh.us/CSPA/pdf/...corporated.pdf
(check out pgs 5, 8 and 9 on the above link, talks about timber harvesting, exemptions and what you need to maintain)
http://www.des.state.nh.us/CSPA/
DEP, Shoreland Questions: 603-271-6876, I spoke to Jeff there before and he was very helpful.