Well although it's not something that happens very often, it does happen. Whenever lightening strikes the ocean, it spreads out across the entire ocean surface because the water acts as a conductor.

Now boats that are nearby, fishes that are close to the surface, or People that are swimming in the area will probably be electrocuted. One lightening bolt can be hotter than the surface of the sun and have over 100million volts of electricity so I don't think you want that coming in contact with your body or anything you might be touching at the time.

The good news is that the potency of the charge reduces with distance from the place that lightening strikes so if you see a storm cloud brewing over the ocean, do well to stay out of the water.

If you happen to be in water and you hear thunder then it would probably be in your best interest to get out of the water and find shelter as fast as possible.