This whale can dive nearly 3 kilometres deep and hold its breath for over two hours

A tagged Cuvier's beaked whale off the coast of California was recorded diving to 2,992 metres, deeper than any other known mammal, and the same species holds the mammalian dive-duration record at roughly 138 minutes on a single breath. Scientists are still studying how their bodies withstand the pressure and oxygen demands of dives that deep, since their typical working dives, around 2,000 metres, already dwarf what any human free-diver could survive.

— Wikipedia contributors, Deepest Dive and Longest Apnea in a Deep Diving Mammal — PLOS ONE, 2014