From 1990 to 2000, a total of 111 carbon monoxide (CO) poisonings occurred on Lake Powell near the Arizona and Utah border. Seventy-four of the poisonings occurred on houseboats, and 64 were attributable to generator exhaust alone. Seven of the 74 houseboat-related CO poisonings resulted in death. Although many of the reported CO poisonings occurred to members of the general public, some poisonings involved workers performing houseboat maintenance. The National Institute for Occupational Safety and Health evaluated an engineering control retrofitted to a houseboat gasoline-powered generator to reduce the hazard of CO poisoning from the exhaust. The control consisted of a water separator and a 17-foot exhaust stack that extended 9 feet above the upper deck of the houseboat. When compared to a houseboat having no engineering controls, study results showed that the exhaust stack provides a dramatically safer environment to individuals on or near the houseboat. CO concentrations were reduced by 10 times or more at numerous locations on the houseboat. Average CO concentrations near the rear swim deck of the houseboat, an area where occupants frequently congregate, were reduced from an average of 606.6 ppm to 2.85 ppm, a reduction greater than 99%. CO concentrations were also reduced on the upper deck of the houseboat. Hazardous CO concentration in the confined area beneath the near swim deck were eliminated. Based on the results of this study, it is clear that houseboats having gasoline-powered generators that have been outfitted from the factory or retrofitted with an exhaust stack that extends well above the upper deck of the boat will greatly reduce the hazard of CO poisoning.