An 18-month-old German Shepherd named Luna fell off a boat in the Pacific Ocean, swam 2 miles to a nearby island, and survived for 5 weeks by eating mice before she was rescued by a team of Navy staffers. She was found to be slightly under-nourished, but in perfect condition otherwise.
In 1973 two men were stranded 1,575 feet below the ocean when their submarine buoyancy tank inadvertently flooded. They were rescued after 76 hours with only 12 minutes of air remaining. It was the deepest underwater rescue mission in history.
A saltwater lake that was cut off from the ocean and is completely filled with jellyfish. As natural predators have been sealed off from the lake, the jellyfish have harmless stingers due to evolutionary regression. Swimming in the lake is safe and permitted. (Source)