Wow, really sad to hear this. It could happen to any of us. We spend enough time in/on the water that we become complaciant and a little careless. It happens anytime one becomes too comfortable in their surroundings. My dad worked around heavy equipment for most of his life and he got hurt a couple times and a lot of the guys he worked with got hurt, some seriously. The usual cause was they skipped some safety step.
As already said, be careful out there guys.