In 2009, fishermen off the coast of South Korea accidentally caught a dolphin in their nets. Instead of returning her to the ocean as is required by law, they sold her to an aquarium.
The dolphin, named Sampal, was made to perform in the aquarium's shows, performing tricks to earn her food. At night, she was kept in a small pool.
Activists and biologists pushed for her release over four years. In 2012, the Korean High Court ordered the 10-year-old dolphin and two other dolphins in captivity be set free.
Instead of dropping the dolphins straight back into the ocean, Sampal and the others were placed in a netted sea pen to rehabilitate them before returning them to the wild.
Sampal managed to escape through a small hole in the pen -- no small feat, as dolphins avoid swimming in tight spaces -- and returned to the ocean.
She kept close to the pen for a while, but then left. Researchers later found her 60 miles away, swimming with 50 other dolphins. Those dolphins are believed to be part of her original pod.