Lightning doesn't electrocute fish

Dear Matthew Alice: When lightning strikes the ocean, why doesn’t all the sea life get electrocuted? Wouldn’t it be just like a radio falling into someone’s bathtub? — C.B., San Diego

Well, if we’re talking the Pacific Ocean, our radio would have to be the size of South America. And even then, it wouldn’t get every last shark and grunion. A lightning bolt can have as much as 200,000 amps of energy in it (1000 times average household amperage), but the bolt, when it hits open water or ground, will dissipate if it has no ionized path to follow. One meteorologist estimated that the average bolt would affect the water within a couple of hundred feet or so of the point of the strike (nearby water would probably boil and turn to steam), but the odds on a fish being within killing range is slim anyway.

Here’s a pretty simplified explanation of what’s going on when lightning strikes. When a storm cloud with a negatively charged underside passes over land or water, it creates a positively charged image area that moves along under it. The insulating properties of air keep the two charges from meeting until the gap between the two narrows sufficiently (which is why lightning tends to hit tall things when it becomes positively charged) or the charges build enough to overcome the ground-cloud gap. At sea, the peak of a wave might be enough to give the bolt a strike point, but it doesn’t even need that. A sailboat, of course, is a sitting duck. And so’s a sitting duck, for that matter. If there’s no nearby charged path for the bolt to zap to, the voltage in the lightning just drains away, on land and sea.