Set a ramp up near some deep water.
Tie a LONG rope to the bike. (Long is important, no rope required if you don't want the bike back)
Ride bike fast up ramp and out over and into water. We used to do it off a dock into Narragansett Bay. You will be wise to throw the bike away from you before you land, and stay clear of the rope.
Don't try this trick at home, or alone. I guess you can try it at home if you have a big body of deep water available, but you might want someone to save your butt if you get injured!
P-
I'm a pretty avid cyclist, and it was long my dream to pedal a pedal-powered boat of my own construction down the Nile. Actually, goldfish1 and I built an attempt at an amphibious bicycle a few years ago. All was going well until a loose nail popped the inner tubes which provided additional flotation...
