RedactedNarrative: I Game Warden was patrolling Lake Mead on land on September 6th, 2017 at approximately 1300 hours.  National Park Service toned a possible drowning located north east of Sentinel Island on Lake Mead. I responded via Patrol Vessel EX3599, I arrived on scene at approximately 1325 hours. Once on scene I found two rental pontoon vessels just off Sentinel Island. I proceeded to tie off my patrol vessel to the pontoon waving at me. 
  
       The three female occupants indicated to me that the victim dove off the bow of the pontoon vessel without a life jacket. Victim proceeded to swim back to the starboard side of the vessel adjacent to the helm. Occupant1 told Victim to swim back to boat and put life jacket on. It was observed by all three female occupants that Victim swimming strokes were weak and he did not look normal. Wife, Occupant1 asked if Victim was ok; he responded yes. Immediately after responding Victim started to sink. Occupant2 was sitting at the helm tried to have Victim grab the oar, but Victim was unable to grasp it. Occupant1 removed her life jacket and jumped in to try and grab Victim, Occupant1 was able to grab him but had to let go due to running out of breath, Occupant1 surfaced and tried to make a second attempt to retrieve Victim but was unable to see Victim the second time. The time was approximately 1300 hours. 
  
       A Good Samaritan vessel stopped and three individuals from that vessel attempted to locate Victim but were unsuccessful. The individuals on the Good Samaritan vessel did not witness Victim diving in the water. 
  
        I was accompanied on scene by National Park Service Vessel. Ranger1 drove the vessel back to Las Vegas Boat Harbor and I followed on my patrol vessel. Once at Las Vegas Boat Harbor, I requested the pontoon vessel to be lifted out of the water so I could inspect the hull and propeller for any indication of trauma. Once the vessel was lifted out of the water, I photographed the propeller area and inspected the boat for all necessary safety equipment. There were six life jackets that were readily accessible, one Type IV and one fire extinguisher that was in good condition. 
  
       NPS ranger Ranger1 and I interviewed subjects at the 704 Ranger station. All three females indicated that Victim did not exhibit any health issues prior to the incident. Victim had previously been diagnosed with Parkinson''s disease, but did not exhibit symptoms as it was in the early stages. Victim behavior and health earlier in the day was normal. 
  
       
  NPS continued to search for Victim in the area by vessel until about 1700 hours; Victim had not been located and remains missing.
  