Dolphins and porpoises
These charismatic sea mammals have the incredible sixth sense of echolocation. Because sound travels better in water than in air, dolphins are able to create a three-dimensional visual representation of their surroundings based entirely on sound waves, much like a sonar device.
This is a necessary adaptation, especially for river dolphins, because vision is often extremely limited in murky water. Dolphins can navigate through a river of tangled branches with ease even if their eyes completely covered.