Except that the Seven Seas Lagoon is not natural, as it is man-made. Unless you mean man-made things that don't look natural?
Excerpt from an article at Mouseplanet:
http://www.mouseplanet.com/7119/History_of_the_World_Part_V
Work also began on Bay Lake. The 406-acre lake was choked with weeds and algae, which were so thick that the water was opaque, even at the surface. An adjacent 185 acres of wetlands were deemed unusable, so they decided to dredge it and create another body of water to extend Bay Lake, creating Seven Seas Lagoon. They built a water bridge to connect the two bodies of water.
The Seven Seas Lagoon dredging provided more than seven million cubic yards of earth, which they used to raise the ground at the theme park site an average of 14 feet. On that site, they built a network of offices, corridors, and utilities, then backfilled with the earth from the lagoon. They would build Magic Kingdom theme park on top of this site. The lagoon, dredged to an average depth of 10 feet, would provide a buffer between the parking area and the theme park, a blessing that had been unavailable at Disneyland because of a lack of land.
Meanwhile, Bay Lake's 3.5 billion gallons of water was completely drained with pumps. A layer of muck eight feet deep was removed from the lake bed, revealing thousands of tons of white sand. The discovery of the sand allowed the construction team to serve two purposes at once. Not only did they clear the bottom of the lake and make it safe for boats and swimmers (for a time), but the sand was removed from the lake bed, cleaned, and used to line the 4.5 miles of beach surrounding the Seven Seas Lagoon and Bay Lake. Once the lake bed had been cleared, they refilled the lake with cleaned water and stocked it with 70,000 fingerling bass.
Seems like quite a feat of engineering to me, I'd liken it to the hanging gardens. man-made natural wonder.
