www.moosepondassociation.org ....... Suggest you take a peek at the milfoil photographs, plus get a good look-see at a milfoil eradication program in western Maine, about 20-miles east of North Conway, NH.
As I recall, your New Hampshire boat registration, up though 2009, included one dollar that went towards milfoil and other invasive weeds eradication. Starting with this last 2010 boat season registration, the NH invasive weed program, which definately includes milfoil, received five dollars from every boat registration, plus your total boat registration price basically doubled between 2009 and 2010.
Since 2008, the State of Maine has required out of state boaters to purchase and display a non-resident invasive plants sticker which costs twenty dollars. Failure to have one can cost $250.
For Maine registered boats, the invasive plants sticker costs ten dollars, and the sticker must be displayed on the boat.
What I cannot find is whether the Maine sticker is a one-time purchase, or a yearly purchase?