One of the most humbling events of my life took place when I was a junior in HS. I was up on a lake with a bunch of friends (all of us happened to be trained lifeguards and very experienced swimmers) and we had been out skiing and were heading back to an area where there were cliffs to jump.
Before making it to the cliffs there was a bridge you crossed under. It was against the law to jump from the bridge, but people did it at times. We were just about to the bridge when we saw two people jump off together. We could tell they landed a bit funny and right away their friends around them started shouting for help. We pulled the boat over and everyone was saying that neither one had come up after jumping in.
All 5 of us on the boat jumped in right away and started looking for the people. One of us found one of the two, and pulled him out and got a boat to take them to shore to do CPR (he lived). The rest of us tried diving down in the water (low visibility, 30+ feet deep) looking for the other person. We were unable to find her.
Because this was before cell phones and the lake was very remote, it took over 30 minutes for any first responders to get there. When the fire department got there, they asked us to borrow our boat to try and drag the lake to see if we could find the body. The boat had a fish finder, and we were pretty sure we “found” the body, but were unable to grab it with the anchor we had (divers found the body the next day in about the same location we had seen on the fish finder).
We found out afterwards that, the people who jumped off the bridge were a boyfriend/girlfriend that had just graduated from HS, and were out partying with their friends and jumped off the bridge holding hands. She jumped “down” and he jumped “up” off the bridge, but they kept holding hands. In the process, she pulled him down right on top of her. It appears that when he landed on her, he just really knocked the wind out of her (no other trauma from what the autopsy showed) and she tried to get a breath of air, but was under water. She took in water and just drowned and sunk to the bottom of the lake.
I still will jump off cliffs, but never do it holding hands with someone. I also think a lot of times what happens is that people land funny and get the wind knocked out of them, and then panic and end up at the bottom.