Having been swimming a few times recently when a thunderstorm developed, I've started wondering what the actual dangers are (please note - I'm more interested in this from a science perspective; I get out of the water if a storm develops, and would advise anyone to do the same). Here's what I think I know of the matter, from some reading on the Internet as well as my own (basic) scientific knowledge, and some questions. Any pointers to research on this would be appreciated.

  • As a swimmer, you're a bit higher than the surrounding water, but not by much, particularly if there's waves. So the risk of a direct strike is probably not significantly increased.
  • The electric current dissipates outwards, near the surface of the water, and can spread some distance (not sure how much)
  • Fresh water is a worse conductor than salty water, so swimming in a lake/pool is more dangerous (in a storm, than in seawater), since the electric current will prefer better conductors.
  • Lightning is extremely loud at the strike zone; the noise alone could cause deafness/ear damage.
  • Being on land (exposed) during a storm is probably more dangerous than being in the water - you're taller, and not surrounded by a conductive medium.
  • How much does the temperature of the water/air increase near a lightning strike?
  • My main question is, if you are in the presence of a direct lightning strike at sea, would the sea water all around you act like a Faraday cage, and take the electric current around your body rather than through it?
  • 2
    $\begingroup$ Well, you are basically salty water inside... Lightning deaths in both sea and fresh water are known. $\endgroup$
    – Jon Custer
    Jan 20, 2022 at 23:58
  • 3
    $\begingroup$ A non-physics consideration: if you get badly injured or even briefly incapacitated, and you're in the water without a vest, you'll probably drown. Lightning strikes apparently have about a 90% survival rate; if a majority of those involve incapacitation for a minute or two, you might have a greater chance of survival on shore even if you're more likely to be injured. $\endgroup$
    – g s
    Jan 21, 2022 at 0:03
  • $\begingroup$ When making your decision I recommend taking into consideration the fact that lightning strikes water more than the ground. $\endgroup$
    – Newbie
    Jan 21, 2022 at 0:34
  • $\begingroup$ I don't think lightning is going to discriminate between a small body of water (you) in a larger body of water. "How much does the temperature of the water/air increase near a lightning strike?" Lighting turns the air into plasma. So a lot. Google is giving tens of thousands of degrees whether in C or F. $\endgroup$
    – DKNguyen
    Jan 21, 2022 at 5:20

1 Answer 1


It does not appear that if you're in salt water you will be safe due to the fact that the sea water is conductive and will somehow protect a person from lightning. Since the human body is itself conductive, it seems that as the electrical energy passes through the water, enough of it should also pass through the person, making it harmful or lethal.

While it might be the case that a person in fresh water is in more danger than someone swimming in salt water (as you stated, fresh water is a poor conductor meaning a human body will absorb the electrical energy of close-by lightning strike) an actual researcher in lightning states that:

"the horizontal distance that the lightning energy [in water] would travel across the surface would depend on the intensity (current) of the lightning and how deep the water is where the stroke hit the water. Water is a fairly good conductor of electrical energy. If you dropped a 120 volt AC line into an 18 foot diameter, 3 foot deep home swimming pool, you very well may be killed. In the case of lightning, multiply the electrical current by thousands, and for the ocean multiply the volume by as much as millions. My guess is that the average lightning strike would electrify a few hundred feet worth of water from it's strike point sufficiently to electrocute someone. However, some current is probably for up to a mile before it is fully dissipated."


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