Stray voltage manifests a lot of different ways, but chronic stress is one of those ways. If you plug in an extension cord that is grounded, and you take a voltmeter that is capable of measuring voltage and very tiny amperage, really, milliamps you can check stray voltage by putting one probe into the water that you are testing and the other probe into the ground opening of the extension cord.
If there is no ground fault from the wall, and you pick up 110 V from the pond you know you have a stray voltage situation. Please be careful not to electrocute yourself. Please note that all voltmeters are not the same: half the voltmeters out there cannot measure voltage in milliamps. 110 V occurring in the milliamp level, can’t even illuminate a lightbulb so the standard circuit tester is useless.
