Like so many blue water cruising sailors, I think nothing of diving overboard for a swim whenever we are in clear warm water even near marinas and docks. When we were meandering through the canals of France a few years ago, I joined friends in fine splashes in the Soame River, the Burgundy Canal and other places. So a few months ago when Beth Leonard* and I were having dinner together and talking about her work with Boating US, I was shocked as she described the research she was doing into several apparent drownings that happened in fresh water and rivers. Turns out stray electrical currents from boats and marina wiring had caused the deaths. I.e. they were electrocutions, not drownings. She went on to say that amazing small amounts of electrical leakage could cause death, as little as one third of the power needed to run a 40 watt bulb. This is not a problem in salt water, only in fresh or brackish water. You can read about her research by clicking here – http://www.boatus.com/seaworthy/magazine/2013/july/electric-shock-drowning-explained.asp
The simplest way to avoid the risk is to swim at least 200 yards from any fresh water marina and away from boats with on-board power.
*Beth Leonard and Evans Starzinger are taking time off from their extensive meanderings on board 47 foot Hawk to top up their cruising kitty. You can read some interesting articles on their website – www.bethandevans.com