Just when you thought it was safe to go back in the water without winding up in a race with Michael Phelps, the Olympic hero is set to test his mettle once again. This time, though, Phelps will be putting his aquatic prowess up against his most dangerous opponent yet: a great white shark.Hey, he has nothing left to prove against mere humans, right? But now in retirement, Phelps does need to parlay his legendary athletic career into high-profile gigs of various sorts, and so it is that he will star in this year’s installment of Discovery’s “Shark Week.”Here is the breathless blurb about the cable channel’s “Great Gold vs. Great White” event, from Thursday’s news release regarding its popular annual shark extravaganza, set to air in late July:

“They are one of the fastest and most efficient predators on the planet: Sharks. He is our greatest champion to ever get in the water: Michael Phelps. 39 world records. 23 Olympic golds.

“But he has one competition left to win. An event so monumental no one has ever attempted it before. The world’s most decorated athlete takes on the ocean’s most efficient predator: Phelps V Shark — the race is on!”