From what I understand (and I could be wrong), the difference with salt vs fresh water is that the salt water can conduct the current easier, so it could go to ground sooner.
With fresh water, it creates a voltage gradient that is stronger at the source, and dissipates as you are further from the source. So if you are swimming away from a dock. you feel a tingling, and as you start heading back towards the dock and apparent safety, you are actually swimming towards the problem, then your muscles get locked up and you can't swim, nor call for help. Some of the reference materiel suggests that many apparent drownings near marinas, docks, etc. may have been caused by undetected intermittent electrical issues.
I'll have to search those links I included for descriptions of all of this, but this is from my memory of researching it a year or two ago, but for some reason I seem to recall that from a number in the order of hundred(s) of feet away from the electrical current source and you could be away from a danger zone in fresh water. I'm not sure if the number is 100, 200, or 500. Before anyone uses this information, I'd suggest that you do your own research. I'm sure the distance varies greatly, depending on the conductivity of the water, the amount of AC current or leakage into the water, voltage involved, and probably several other unknown factors.
Here's the background on the 'green light' or 'safe to swim' warning devices:
https://www.electricshockdrowning.or...t-devices.html
Quote:
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Monitoring devices used as a “green light” to indicate it is safe to swim around electrified docks will put a lot of people at great risk. Staying out of these potentially dangerous waters for recreation is the only way to eliminate the risk. If used solely to alert an owner that there are electrical safety problems on the dock, then the ESDPA fully supports their use. But NEVER as a “green light” for swimming or other in-water activity.
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Personally, I think a private dock is a much different story than a shared dock with multiple boats.
If anyone comes up with more information, such as a report that states a safe distance in fresh water, I'd like to know the source please. For example, I'm told that a popular lake marina doesn't allow swimming from their docks. but has a nearby beach or designated area where swimming is allowed.
This link says no recreational swimming within 150 feet of a dock with shore power:
https://www.electricshockdrowning.or...tober_2019.pdf
Here's another presentation on ESD that is easier to read as it's all slides and bullet points, and has minimum 'fine print'. It also states 150 ft as a minimum distance from a shore power dock:
http://electricshockdrowningmn.com/D...08-16-2018.pdf