Yes, I am in fresh water (Lake Erie) exclusively. I'm in a state run
marina and I suspect if I asked them to check for 'stray current' first
they'd laugh at me, then they'd put me on the standard 6 month waiting
list - at which time, my boat would be out of the water for winter
storage! Sorry I'm being sarcastic, but I don't expect much action
from the marina.

Is there a way I can check for stray current?

Also, you say shore power cords in the water can cause a problem? How
close do they have to be?

One more thing, I like to back my boat into the slip so the outdrives
are really close to the shore power receptacles all along the dock. I
wonder if that could have something to do with it?

Thanks, this is interesting.