Does lightning fry fish?

10 March 2014

Question

When lightning hits the sea or a lake, do any fish nearby get electrocuted?

Answer

Hannah - So, why don't we see floating electrocuted fish following a thunderstorm? First up, some facts. Lightning is a massive electrostatic discharge, the sudden flow of electricity. During a thunderstorm, regions of positive or negative charge build up within or between clouds and the surface of the planet. This charge is eventually discharged by a lightning flash or strike, carrying a whopping 30,000 amperes of current and transferring 500 megajoules of energy. This is the equivalent energy striking in a split second as a colossal 1,400 100-watt bulbs running for an hour. So, since humans are concerned about being frazzled when lightning strikes on land, aren't fish worried in water? Over to the expert.

John Jensenius - My name is John Jensenius. I'm a lightning safety specialist with the National Weather Service in the United States. Really, when you get down to it, you have to look at what happens when a thunderstorm develops and what happens just prior to the lightning strike. There's a charge that builds up in the cloud and there's an opposite charge that builds up on the surface of the water. So, when lightning flash occurs, the discharge discharges along the surface. So, the effect of the lightning is pretty much contained to the surface of the water and in fact, the fish that are swimming below the water are safe. They're completely unaffected by the lightning.

Hannah - And listener Erik Sandberg agrees. He says that the lightning electricity will mostly stay on the surface of the water. He also says that he thinks it's to do with the fact that the water is such a good conductor and the electricity will quickly be dispersed or spread-out to the surrounding water close to the surface.

John Jensenius - Well, [salt] water is a good conductor of electricity, and that's one of the reasons that the charges can move to the surface of the water and it is true when lightning strikes the water that discharge literally spreads out along the surface. Of course, with the fish below, they should be safe.

Comments

ok, I get the concept of spreading over the surface, but it doesn't explain why if the water and salt are such good conductors why doesn't the electricity travels downward as well as on the surface.

For an electrical current to flow particles must be present that are capable of carrying a charge and being mobile. In a wire this job is done by electrons, which are the negative particles in atoms. A power source - like a battery - pushes electrons into the wire at one end of the circuit and the electrons transfer the charge - producing a current - around the circuit as they move.

In water / the ocean it's different in that there are not lots of free electrons around to carry the charge. But there are lots of ions - which are charged atoms; for instance there will be sodium ions (Na+)  and chloride ions (Cl-) from the sodium chloride (NaCl) that makes the sea salty.

These particles can move through the water carrying a charge. This is how the electrical energy is dissipated through the water.

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