S4 E1 • American Killers

In the suspense-filled two-hour premiere, Jeremy Wade treks across the United States in search of deadly river monsters living in the nation's waterways. Wade ventures from the popular Indian River Lagoon in Florida where unsuspecting water enthusiasts are faced with what could become a modern day Jaws, to the Lake of the Ozarks in Missouri, where underwater hunters have reached man-eating proportions.

S4 E2 • Pack of Teeth

In Southern Africa there are rumors of a terrifying river monster lurking in the eerie waters of the Okavango Delta. Witnesses say the fish have shark-like teeth and hunt in frenzied packs on schools of fish — and maybe even on human bodies. It sounds mysteriously like the work of giant piranhas, but there's nothing like that here. Or is there? Jeremy Wade sets out to uncover the truth.

S4 E3 • Invisible Executioner

It's common knowledge that crocodiles and hippos are deadly predators in Zambian waterways, but it seems there's another monstrous beast stalking the treacherous Zambezi River. The locals call this river monster "the Mazunda" but Jeremy Wade is unfamiliar with any fish by that name. Will he uncover what the sinister creature — said to be able to swallow a child — really is?

S4 E4 • Asian Slayer

When Jeremy Wade travels to India's Himalayas to investigate grisly river attacks, he is surprised to learn that the suspected culprit is a sacred animal. Does he heed warnings from the local people that he'll be cursed for life if he touches the creature, or will he pursue his need to solve the mystery?

S4 E5 • Russian Killer

The eerie disappearance of three men in far eastern Russia proves to be a baffling case for Jeremy Wade. His first visit to Russia takes him on a three-day trip to the Amur River where he seeks to uncover what happened to the fisherman and others who have met their demise on these waters. The prime suspect is a predator that can top a ton and exceed 18 feet in length — yet for some reason, not a soul will help him find it. Stonewalled at every turn, Wade begins to believe there is there a dark secret he's not meant to discover.

S4 E6 • Mongolian Mauler

In Mongolia, Jeremy Wade hopes to reel in a rare river monster that’s become legendary. Pound for pound, this man-sized monster is said to be one of the world's strongest fighters. Could the rivers here still be home to a beast that many have heard about but few have seen? While Wade is on the hunt, he may be hunted himself as armed outlaws lurk in the wilderness surrounding the remote river.

S4 E7 • Phantom Assassin

Jeremy Wade returns to Australia's croc-infested Fitzroy River for one of his toughest quests yet — to catch one of the world's rarest fish. This shark is so elusive it was only discovered ten years ago, and so rare only a handful of people have ever seen it. Almost nothing is known about this endangered beast. Could it be a man-eater? The expedition turns Wade's knowledge of freshwater killers upside down as these animals seem to break all the rules.