Even though most underground electrical lines are marked, some are not. Visible wires are equally unsafe. Contrary to popular belief, the vast majority of high-power wires are not insulated, although they sometimes have a very thin coating to prevent weather wear. But that coating is easily arced. Special care should be taken whenever you're close to these wires.
Tree trimming or removing wet leaves from the roof, for example, can be hazardous.
The minimum safe distance for any object, plant or person from the least powerful overhead lines is 10 feet. News reporter Alpert's van antenna appeared to be dangerously inside that range even before it was extended. Turn off the power. Keep appliances away from water. It sounds obvious, but thousands of accidents occur every year involving water and home appliances.