Swimming in a marina or near private docks can be dangerous because of reversed polarity that can lead to electrical shock from one of the boats.
Reversed polarity can energize all ground connections causing electrical current leakage into the surrounding water around boats.
The stray current can also cause corrosion to underwater metals to your boat or the neighbor’s boat.
Modern electrical receptacles are polarized allowing the plug to be inserted in only one direction.
However the receptacle still needs to be properly grounded.
Consider checking the plugs around your boat, dock and house.
Portable polarity testers are inexpensive and may be purchased in the electrical supply section in many stores or online at the link above.
You can find out more about the very real dangers of Electric Shock Drowning HERE.
Boat Smart from the start and take a boating course.
The United States Power Squadrons offers many courses such as weather, seamanship, navigation, marine mechanics and marine electronics.