While I agree that sounds rude, and may not be legal, waterfront property owners do have more rights than other citizens to the waters adjacent to their property. NH Supreme Court decisions show that waterfront property owners have some common law rights to to these waters. That the state owns the lake is not the point.
http://bearisland.org/legal.htm
I know many boaters bristle at this idea but look at it this way. A waterfront property owner can construct a dock, put out a swim line, install a water intake, drop a mooring or float a swim raft in the water next to their property, but nobody else can. This shows they have more rights to that water than anyone else.
There was also a new rafting law that addressed this but I don't know if it passed or exactly what it said.