Heck, Charley, I grew up on the Mississippi. When we wanted to reverse the direction of the boat (up to 20 feet long, and a johnboat) we'd yell, "Quick, quick, go backwards or something!" This was uaually followed by a grinding sort of sound as the boat ran up on the log/sandbar/floating house/other boat/mine/buoy/locomotive/barge or whatever.

Other commands were "Quick, turn around!" and "Head for shore, the drain plug's failed!" and "Holy #@$%!! what #@#$@!!*% was that?"

To bring this back to the thread topic, I've seen trapped gases released from sunken vegetation in sloughs, bays, and such in rivers. Lots of 'em stunk, too.