Abstract: At 2:30 p.m. on October 27, 2020, Employee #1, Coworkers #1 and #2, and their supervisor, divers employed by a civil engineering construction company, were engaged in a diving operation at a lake dam. They were assigned to conduct inspections and repairs to several gates and chains. During a solitary dive with an umbilical supplying breathing gas and video, Employee #1 climbed down a long ladder to the water's surface. He then descended into the water, sliding down the chain with his right hand while feeling the side of the dam face with his left hand to guide his way down. At a depth of approximately 15 to 20 feet, his left hand came into contact with a 10-inch hole in the dam's face that led into a Penstock Pipe. Differential pressure caused the employee's left arm to be sucked into the pipe up to his shoulder. He cried out and then went silent and unresponsive. The dive supervisor attempted several times to communicate with Employee #1 but received no response. The supervisor instructed Coworker #1, the backup diver, to go into the water. Coworker #1, after reaching Employee #1, reported that Employee #1 remained unresponsive with no signs of breathing. Coworker #1 was unable to free him from the pipe. Several dam employees were called to the scene, and one of the dam operators closed a valve which released the diver from the pipe. Coworker #1 brought Employee #1 to the water's surface, where he was attached to the emergency retrieval system, removed from the water, and placed on the main deck where emergency medical technicians were standing by. Employee #1 was transported to the hospital, where he was declared dead. The subsequent investigation reported that mechanical asphyxiation may have been the cause of death. At no time had Employee #1 lost air.