Sharks, the world's fastest and most efficient predators. Michael Phelps, our greatest champion to ever get in the water. A Shark Week first brings an event so monumental, no one has ever attempted it before. Phelps vs Shark - the race is on!

Shark Week's Paul de Gelder teams up with Dr. Mark Meekan to travel to the sharkiest places in the world, Cobourg Penninsula in Northern Australia. They want to know what happens when 14-foot crocodiles moves into shark infested waters?

Early November, pregnant giant hammerheads arrive off Bimini, in the Bahamas and Shark Week's Dr. Tristan Guttridge wants to know why? And he and his team even perform the world's first ever ultrasound on hammerheads to find the answers.