Aha! its not tethered to the beach, you drag along the pump..

So how's it work?
Ramke doesn't offer any details at his website, but according to Der Westen, a floating pump powered by a four-stroke engine (115 to 130 horsepower) sends water through a 140-foot-long hose to a pair of nozzles mounted on the "jet pack." It looks a lot like the "personal propulsion device" Canadian inventor Raymond Li patented about two years ago. Li calls it JetLev, for jet levitation.
Li has touted the safety of the contraption, noting that the pack floats, it has no moving parts and the water shoots out of the two nozzles at no more than 100 PSI. You're also no more than a few dozen yards above the water if something goes pear-shaped. That makes the risk a little more acceptable than, say, strapping on a hydrogen-peroxide pack and jetting across a gorge like Eric Scott or soaring over the alps or across the English Channel on homemade jet wings like Yves Rossy.
Ramke says the JetLev-Flyer is a breeze to operate, and the 100,000 ($128,000 U.S.) price tag includes "detailed instructions by a qualified personal trainer." At that price, its no surprise that Ramke told Spiegel most of the people buying them are Russian oligarchs.

Reality..What a concept!