If you think using a chain saw while climbing a tree is dangerous try using one of those hydraulic saws to clear out old rotted piers in the murky waters around a marina the visibility could be less than a foot or 2 even with a powerful dive light. People throw everything over board sometimes those who lease permanent slips of berths in the boat houses will sink things like old bed springs toss their damages sail lines cables and other things like ruined outboard motors just about anything you can imagine. and when it comes time to replace the piers of underwater bracings you have to go down and fight through all of that junk. I wore a dry suit most times instead of my wet suit when I had to dive in or around the slips because the dry suit was thicker and less likely to rip if snagged but a puncture could men it would fill up with water when it did you had to loose some of the weight off the weight belt that was compensating for the extra buoyancy the suit had. I never used a chain saw under water because we didn't have one we would use a pneumatic grinder with a saw blade probably even more dangerous that the chain saw would have been.