In addition to Huds' notice above. Boaters who enter Canada and then wish to return to the US are now REQUIRED to present a passport when re-entering the States.
"Effective June 1, 2009, all U.S. citizens are now required to present a passport book, passport card, or
WHTI-compliant document when entering the United States.
Please Note: Children under age 16 will be able to continue crossing land and sea borders using only a U.S. birth certificate (or other form of U.S. citizenship such as a naturalization certificate.). The original birth certificate or a copy may be used. See the Department of Homeland Security's
Ready, Set.. Go! for more information on the changing travel requirements."
I can't wait to hear the conversation at US Customs when some lucky boater is refused re-entry into their own country.
Here's the link.
Western Hemisphere Travel Initiative