Some shark species can survive in freshwater as well as salt. Zeb Hogan tries to track down the biggest and rarest Australian examples.
Two massive pond projects take the team to Jacksonville, Florida. Larry Payne wants a 30-foot pond and a 2,000-pound cypress bench.
Aquatic ecologist Zeb Hogan wrangles what may be the biggest freshwater species in the world, the Mekong giant catfish.
A team of scientists attempts to unlock the secrets of the Congo River by investigating the ravenous predator that prowls its waters.
Hundreds of silver fish rain down on a remote community in Australia, whales seem determined to strand themselves, and Alpine ibex scale a dam.