Dr Zeb Hogan, National Geographic Explorer and an aquatic ecologist goes on his journey to find the largest freshwater fish in Australia – the freshwater sawfish, a cross between a shark and a chainsaw. These amazing monsters are nearing extinction but our continent is a stronghold for this elusive fish. Zeb gets in the water to learn about the sawfish's amazing hunting technique, stunning prey with its saw-like rostrum and then eating it whole. Zeb teams up with a local scientist, David Morgan and the indigenous Jarlmadangah Rangers, to catch and study the monstrous sawfish in the Fitzroy River in the country’s northwest. Zeb travels deep upstream into the desert where freshwater pools hide huge predators like the saltwater crocodile and bull sharks. Zeb and the team follow the sawfish migration from the estuary upstream and back again until they return to the sea. He tags and releases many sawfish, from a month old baby to a 2.2-metre megafish on its way to the ocean where it could someday grow to be a monster 7-metre fish.