When the motor on a PWC is running, the impeller can cause severe internal injuries. The impeller is a rotating device that draws water into the engine and propels it out through the exhaust. If someone falls into the water while the impeller is running, it can catch their clothing or body and pull them into the engine, causing serious injuries or even death. For this reason, it's important to be careful around a PWC when it's running and to never let anyone stand in front of the engine intake.