Motorboats can release CO at very high concentrations. The CO can accumulate in and around the boat when idling, and can even be dragged behind the boat in what’s known as the “station wagon effect”. CO on houseboats can be released not only by the motor, but also by the onboard generator. Many deaths have occurred on houseboats due to CO accumulating in cabins, and in areas around (and under) the boat where children often swim.