I have found several popular articles (e.g. ScienceDaily, The Globe and Mail, and WebMD) indicating that children with Autism have a significantly elevated risk of drowning. The general theory seems to be that the calming affect of water combines with a lack of situational awareness common in people with Autism to create a "perfect storm" situation in which the child is presented with highly appealing decision opportunities that they are not fully able to assess. A simple online search for "autism and drowning" turns up tons of articles and discussions about the risk of drowning in children with Autism.
Has a substantially elevated risk of drowning been shown to exist or not exist for adults with Autism? That is, is the risk of drowning for children simply more socially relevant today (e.g. drowning out any studies and warnings of potential linkages for adults), or is there substantial reason to believe that the maturity that comes with age does or does not reduce the risk of drowning to control group levels?