This is not my theory, it was created by someone else.
It was June 2, 1946 when the first nuclear test occurred at Bikini Atoll, but it certainly wasn't the last. Between 1946 and 1989 there were a large number of atomic explosions which hit the uninhabited islands, detonated by the United States.
As a result, several radioactive isotopes - the most notable being Strontium-90 - were released into the atmosphere and soon irradiated the waters surrounding the islands.
In 1976, during a cleaning process it was discovered that there was life located at the bottom of the surrounding ocean. Using specialist radar technology it was determined that these creatures were unusual because they had adapted so as to inhabit artificial constructs within large communes.
In the short while Bikini Atoll was temporarily inhabited (prior to when Caesium-137 began to take effect in 1982), US troops were known for leaving things behind, including buckets, chests and tin-cans. When one of these islands sank as a result of the "Castle Bravo" nuclear test on March 1, 1954, these items ended up at the bottom of the ocean.
For some reason the sea-creatures encountered in the 1976 expedition were more intelligent than usual. They had utilized this waste and had began to live within them, treating them almost as part of their natural surroundings. Animals such as crabs began a primitive form of civilization similar to our own.
Some land-animals were sent down in specialist suits so as to adapt with these sea creatures. This selected group continued to be exhibited up until 1998. A person working for the corporation Nickelodeon in a tour funded by the company was one of the few people who saw these creatures in action. This eventually provided the inspiration for a certain popular children's television program.