The Leviathan

The Leviathan is a massive marine arthropod, located near the tip of South America. It is estimated by two SCP Foundation scientists to be between 2000 kilometers to 8000 kilometers in length. An archipelago with an unknown name is situated on top of its back plates. It moves less than one kilometer per week, through an unknown propulsion method. Seismic tremors indicate that it undulates every three months, causing minor shifts in the islands terrain, suggesting that the creature is probably dormant.

The SCP Foundation is currently preventing public access to the archipelago due to its large number of endangered bird species. NASA is currently also allowing the Foundation to edit satellite footage to hide evidence of the archipelagos movement. After the NOAA discovered the low-frequency sound, the Foundation is now attempting to prevent civilian teams from discovering the origin of the sound.

History
Although The Leviathan is thought to have existed since the pre-Cambrian era, it's archipelago was first claimed by an unknown individual during the 17th century. Later on, Mobile Task Force Gamma-6 investigated the area in the 20th century. One of the members noticed that the archipelago has moved 3 kilometers from its original location. At first it was thought to be quick-moving continental drift, but a mission performed from a United States Ship revealed it's true nature as being situated on the creature.

After this discovery, the former United States Ship was deliberately sunk by the SCP Foundation with permission from the American government. The Foundation then proceeded to enact it's current containment procedures.

During the last decade of the 20th century, the NOAA discovered a low frequency underwater sound near the location of the Leviathan. Although an embedded Foundation agent attempted to prevent mass exposure, it was leaked into the mainstream.

Trivia

 * The image used to represent the sound created by the Leviathan is a spectrogram of the Bloop, a real sound detected in 1997 near South America, thus implying that the Leviathan was responsible for the Bloop.