Fontana police said its officers and Fontana fire officials responded to Gordy's Marine at 320 Lake Street around 8 p.m.
The Wisconsin Department of Natural Resources said three people were trying to dock a boat. One of them, a 57-year-old Wisconsin woman, fell into the water.
Emergency responders were able to free the woman from the propeller, but she was pronounced dead on the scene, police said. Her identity was not immediately released.
Police said the boat's driver cooperated with investigators, and charges have not been filed.
The Wisconsin Department of Natural Resources said it is investigating the incident, which the agency called an accident.