I bet that if I strung a wire across the canal and checked the neutral at my neighbor's house there would be a very significant voltage difference and the "ground" would be different too.
Around here, a voltage difference is pretty much guaranteed.
I once measured more than 100 volts between an insulated ground wire and a buried ground wire over a couple hundred feet. It was close enough to 110 volts that I went back to the source to check the connections and found the power hadn't been turned on to that panel.
When the two grounds were connected, the spark was visible in the daylight, so there was some amperage with the voltage.
