The Delaware Department of Natural Resources and Environmental Control has come up with a fantastic use for disused subway cars—they're dumping them off the coast to create new coral reefs. Results have already been positive, with parts of the ocean floor benefiting from more sea grasses, sponges and blue mussels.
Natural reefs are constantly under threat, but new, synthetic reefs can help with the deficit, and by providing a solid surface for reefs to grow, a great benefit can be given to the ecosystem that lies beneath. Currently, the rejuvenated reef consists of some 700 sunken subway cars, and that number continues to grow. Now, divers, don't get all excited—it's not a new park for you to mess about in, it's a coral reef, so stay out. [Inhabitat; Thanks, Nancy!]