RedactedNarrative: Vessel 1, a 20ft open motor vessel, FL0437KA, was being operated in the area of Bear Cut. According to statements given by Operator 1 and Occupant 1 they were underway when the vessel experienced an engine casualty and began taking on water through an unknown means. Operator 1 stated that he set the anchor and had the occupants of the vessel put on PFDs. Operator 1 also informed me that the vessel had no effective means of de-water as the bilge pump was not functioning. The vessel soon took on water and sunk in shallow waters (3-4Ft) near Key Biscayne. FWC Officers responding to the distress call were able to retrieve all occupants without further incident and no injuries were reported. It is determined that the cause of the accident was due to water intrusion into the vessel, although by what means has not been determined. Compounding factors such as not having an effective means of de-watering and the outboard motor suffering a casualty, potentially added to the sinking of the vessel. Operator 1 was provided with relevant case information prior to clearing the scene.