RedactedNarrative: On July 29th, 2015 at approximately 430 hours, a 55' 1976 King Craft Houseboat partially sunk into Lake Powell while the vessel was beached at Hall's Creek Bay. A 20' 2001 Bluewater Mirage Motorboat that had been securely tied to the aft of the houseboat also sank as a result of the houseboat taking on water. SUBJECT and his traveling party were sleeping aboard the houseboat when it rapidly began to take on water and sink. Passengers on board the houseboat were all able to evacuate to other vessels and/or land. The houseboat sank until the stern section of the craft came into contact with additional ground located underneath the surface of the water. It could not be determined on scene what may have caused the vessel to sink.
  
  Details of Incident:
  On July 29th, 2015 at approximately 457 hours, dispatch called me to report that two vessels were sinking in Hall's Creek Bay. I requested that Rangers also be called out to respond to the incident and meet me at Hall's Crossing Government Dock. Around 530 hours, all three of us responded in NPS Vessel 2511 to Hall's Creek Bay, I spotted a partially submerged houseboat (later identified as Vessel #1) that appeared to be resting at a significant angle near a rock island.
  
  Upon arriving on scene, I determined the two vessels involved in the accident were a 55" 1976 King Craft houseboat (Vessel #1) and a 20' 2001 Bluewater Mirage Motorboat (Vessel #2). The operator and owner of the two vessels was identified. As I was collecting information regarding the incident, one of the passengers aboard the houseboat expressed that she was experiencing chest pain and was light headed (See corresponding emsChart for additional information). Rangers tended to the patient, while I requested ALS (Ranger) to respond as well. Ranger responded to the scene to assist with the medical incident. At that time, no other passengers mentioned that they were injured as we checked on the status of the group.
  
  SUBJECT, in his verbal statement, indicated that the houseboat had been left in dry storage at Bullfrog over the winter and launched approximately six days prior to the accident. He further stated that the party had proceeded to Hall's Creek Bay and established their camp at that time. SUBJECT said around 430 hours, the houseboat began to rapidly take on water and the stern abruptly sank into the lake. The entire party was able to evacuate, but SUBJECT wasn't able to untie the motorboat before it was pulled into the lake by the sinking houseboat.
  
  Approximately the rear third of the houseboat sank into the lake before it came into contact with additional ground underneath the surface of the water. Additionally, several large inflatable water accessories had become wedged underneath the upper deck of the houseboat, leaving the houseboat in an unstable position. The motorboat was pulled nearly entirely underwater, as only the tip of the bow was protruding above the water. Aramark Executive Services were contacted after Rangers cleared the scene. Both vessels were successfully recovered by Aramark that evening.
  
  The cause of the accident was not determined on scene. It was mentioned by a passenger that the bilge pump for the houseboat had been running fairly regularly earlier in the trip. Vessel #2 did not appear to experience any kind of mechanical or equipment failure, but was pulled underwater as it was tied to vessel #1. On August 1st, SUBJECT emailed me with additional information regarding the incident. He indicated that two passengers had sought treatment from doctors for injuries (soreness, stiffness, and bruising) that were likely sustained (but not indicated until days later) as a result of the frantic evacuation from the sinking houseboat.