When you are frolicking at the shore and a thunderstorm
is heard in the distance most sane people pay heed an leave the scene for
safer quarters. Most people know that lightning is more likely to strike
a person standing in water that if they were in a secure building. Because
they are well grounded by the water and present a "high" object compared
to the flat surface the strike potential increases.
Divers do not always get the same warning. They may enter
the water with the sun blazing and no hint of a thunderstorm in the area.
After 45 minutes of diving the conditions may change without the diver being
aware of it. So, what should you do if you are underwater and a thunderstorm
rolls in? Should you come to the surface? And, what would happen if lightning
struck the lake with divers in the water? Would they experience a "hot squat"?
When a diver is suspended in water they are not a target.
They do not present a direct link to the Earth as they would if they stuck
their head out of the water and lightning struck that. If there was a danger
if electrocution then many fish would be killed each time lightning struck
bodies of water. Now, if the diver was close to the surface, let's say no
more than 5' underwater, and lightning struck immediately above, then there
is the possibility the diver (and the surrounding area) would become instantly
charged and then immediately discharged which could become lethal. The chance
of that happening would be less than having lightning travel down a bathroom
pipe and hit someone sitting on the toilet.
It has been the author's experience to come near to the
surface during a violent thunderstorm. Lightning flashes were visible from
underwater. The heavy downpour produced visible raindrops pounding into the
lake's surface. Needless to say we did not surface. Instead we used our compasses
to go to the nearest shore and then traveled along that to the exit point.
If you have the air to remain underwater it would be better than swimming
on the surface. But, swimming along the shore seems to be safer than swimming
at the surface in the middle of the lake.