In the middle of the ocean is a yacht. Several corpses are floating in the water nearby.
A group of people were on an ocean voyage in a yacht. One day, they decided to go swimming — they put on their swimsuits and dove off the side. They discovered belatedly that they have forgotten to put a ladder down the side of the yacht and were unable to climb back in, so they drowned.
Alternate Solution (choose one):
The same situation, but they set out a ladder that was just barely long enough. When they dove into the water, the boat, without their weight, rose slightly in the water, putting the ladder just out of reach.