He and his sister ventured into a restricted area at Yellowstone, looking for a hot spring to go swimming in. He fell in, and either drowned or got boiled to death. A freak lightning storm prevented rescuers from retrieving the body until after about 24 hours. When they returned to the water pool, the body had mostly dissolved away. Apparently the water was not only hot, but also extremely acidic.
The sister apparently recorded some video of the incident on her cell phone. The Park Service has the phone and will not release the video to the public.
The 20-something year old lad deserves a Darwin Award for 2016!