Whether you need a passport for the Maid of the Mist depends entirely on which side of the border you are starting from and whether you plan to cross over. If you are already in the United States (Niagara Falls, NY) and you take the Maid of the Mist boat tour, you do not need a passport, as the boat departs from and returns to the American shore. However, if you are on the Canadian side and wish to take the Maid of the Mist (which only operates from the U.S. side), you must cross the Rainbow Bridge or another border crossing, which requires a valid passport, NEXUS card, or an Enhanced Driver's License. Conversely, the Canadian version of the tour is called Niagara City Cruises (formerly Hornblower); if you are in Canada and take this tour, you do not need a passport. The confusion often arises because both boats enter the same basin near the falls, but they never dock on the opposite side. If you intend to see the falls from both the U.S. and Canada, a passport is an absolute requirement for the border crossing.