Answer: An Aircraft Carrier

Humanity has long appreciated the role that reefs play in the ocean ecosystem, and even as far back as medieval Japan, people were using rubble to create artificial reefs to grow kelp and serve as a home for fish. Since then, various materials have been used for artificial reefs. Some have been used with great success, like turning decommissioned subway cars into artificial reefs. Others, with less success, ranging from poor adoption by fish to outright ecological disaster—as is the case with misguided efforts in the 20th century to turn old tires into reefs.

One particularly successful artificial reef, and the largest single man-made reef in the world, is the one created from the former USS Oriskany. In 2004, the Navy gifted the ship to the state of Florida to sink off the coast. In 2006, after a year of cleaning and hazardous material removal (all of 2004), then waiting for EPA approval, the ship was sunk after being carefully rigged with explosive charges by Navy experts to drop it precisely into location on the ocean floor off the coast of Pensacola, Florida. The photo here documents the detonation of the charges and the beginning of the sinking process.

The 44,000 ton aircraft carrier flight deck is located at approximately 145 feet below sea level (although the ship’s control tower reaches up to roughly 80 feet below sea level). The area is open to divers, but entry into the flight deck requires additional training and gear. Divers affectionately refer to the location as “The Great Carrier Reef”, a pun-filled nod to Australia’s natural Great Barrier Reef.