Final answer:
The most likely place a swimmer could get a fatal dose of carbon monoxide (CO) is in an enclosed space with poor ventilation, such as an indoor pool area or a poorly ventilated pool house.
Step-by-step explanation:
In the context of swimming, the most likely place a swimmer could get a fatal dose of carbon monoxide (CO) is in an enclosed space with poor ventilation, such as an indoor pool area or a poorly ventilated pool house. CO is an odorless and colorless gas that is produced by the incomplete combustion of fuels like gasoline, propane, and natural gas. When these fuels are burned in enclosed spaces, the CO can build up to dangerous levels. If a swimmer is exposed to high levels of CO for a prolonged period of time, it can lead to symptoms such as dizziness, confusion, unconsciousness, and even death.