Sink or swim...or get a machine to do the dirty work. The BladeFish SeaJet is a battery-operated underwater scooter for zippin' around with the fishies during SCUBA and snorkeling adventures. "Scooter", rather than "jet", is the operative word for the BladeFish, which, at peak speeds of around 3 mph, probably isn't going to be of much assistance during frantic attempts to outswim sharks and cantankerous octopi. However, since the average non-motorized human swims only 0.5 mph, it will help users cover more ground during dives, and faithfully fulfill its duty as a rad $700 beach toy.
The SeaJet 5000 (pictured; there are also 1000, 2000, 3000, and 7000 models with varying speeds and levels of power) runs on a rechargeable Lithium Ion battery, which claims to hold its juice for 1+ to 2 hours at a time, at a depth of up to 130 feet. It has 3 speeds, and is buoyancy adjustable via specialized floats. Weight is 10.2 pounds, dimensions 15" x 15" x 6".