At 1037 hours, Charles County Communications dispatched a motor vehicle collision with a vehicle in the river and a report of one trapped.  Rescue Engine 113, Truck 11, and Chief 11A responded, as well as the remaining assignment.  Boat Support Unit 8 was the first to arrive and advised that the vehicle was only partially submerged.  The patient was not trapped.  Chief 11A held Company 11 units while Emergency Medical Services evaluated the patient.