Free divers can hold their breath for as long as 5 minutes and I have heard of longer than that. Free diving blue fin tuna fishers use a spear gun and no tanks just shoot and hold on I was watching a program a few years ago about it they said one guy stayed under water for 7mins and 23 seconds he wouldn't let go of the spear gun till the tuna stopped swimming. I know of guys that would high dive off rocks in to a lake that had caves down about 20 feet they would dive and swim through the caves there were 2 exits 1 you had to swim about 20 feet and the second exit was another 40 feet. try that with out fins on. I think the lake was Hillock Lake. The Canadian underwater council help super dive 1986 there I was there. water skied to the cliffs from the campsite it took about a half hour to get there. I don't even know if they still hold these dive competitions any longer. They were a lot of fun party half the night so you could go diving the next after noon.

Bill