This shows the dangers of low head dams 

I'll be sure to go by high head dams only, thanks!

Nice visualization of the danger

-"the boil" (air bubbles) makes objects less buoyant, - because the water is less dense. so basically even if you are swimming you will sink.

The drowning machine

Now you can comment on this video. Low head dams are dangerous. Don’t go near one. This was just somewhere in Yorkville rapid

This should be required viewing before anyone can buy a kayak or raft.