A 48-year-old Utah man died of unknown causes last Saturday while scuba diving in the Black Canyon area of Lake Mead. Early that afternoon, park dispatch received a marine band radio call reporting a diver floating face down in the water. Rangers and Nevada Department of Wildlife wardens responded and began CPR, but they were unable to revive him. According to witnesses, the man was a mixed gas dive instructor who was diving with a group to depths of around 350 feet when he ran out of air. His dive partner shared a spare tank as the two began their ascent. At some point, the man separated from his safety line and made a free ascent without gas. The other divers ascended using normal decompression without incident.