In the September/October, 2003 issue of Public Health Reports, Marilyn L. Browne and collegues described environmental and personal risk factors associated with 216 watercraft-related drownings occurring between 1988 and 1994 among New York state residents. Carbon monoxide (CO) exposure was not one of the risk factors identified as meaningful for future reduction in such drownings. As part of an ongoing investigation of boat-related CO poisonings in the United States, we have identified 503 severe CO poisonings occurring primarily between 1990 and present. Of these poisonings, 101 resulted in death, and 46 of these deaths were CO related drownings. One of these drownings occurred in New York in 1996. This woman voluntarily entered the water to swim and drowned after 10 minutes in the water. Because the Medical Examiner analyzed the blood specimen for carboxyhemoglobin (COHb), which was found to be 62%, CO exposure from the boat's operating propulsion engine was listed as contributory to her drowning. During an extensive review of U.S. National Park Service records of boat-related drownings that occurred between 1994 and 2002 at Lake Powell (U.S. National Park Service Glen Canyon National Recreation Area), we determined that 11 of the 26 (42%) boat-related drownings were related to CO exposure. These drowning victims had measured COHb concentrations ranging from 26% to 59%. Nine of these victims voluntarily entered the water, one collapsed while on a platform (fell overboard), and one death was unwitnessed; thus, no information was available about his entry into the water. These drownings occurred because boat design features intended for occupancy (e.g., swim platforms, extended rear decks) and exhaust terminus configuration place people close to propulsion engine and/or on-board gasoline-powered electrical generator exhaust. Studies conducted since 2000 have shown that these engines, most of which have no emission controls, produce CO-rich clouds with concentrations greater than 60,000 parts of CO per million parts of air (690 times the short-term exposure limit recommended by the World Health Organization) measured outside the cabin area of the boat.