Skydiver here. I'm not familiar with this particular event, but that does seem rather high even for those years. In the USA we average ~1 incident per 250,000 sport skydives. Tandems are around 1 in 500,000.
Yeah, about that... None of what you said would work. People think water is this "cushion" like thing. In reality it is as solid as a brick unless the surface is broken (the mattress is not enough). A human would just end up breaking every bone in their body attempting to do this.
Although it has always been a good idea for something like this. I'd be surprised if the FAA allowed such a thing to happen. It would have to be a permanent NOTAM, and in an already existing no-fly zone for personal aircraft.
You can find the USPA incidents here: https://uspa.org/Find/FAQs/Safety