Dumping old New York City subway cars into the Atlantic Ocean (A and B) may look like irresponsible waste disposal. But environ­men­tal­­ists are thrilled about it because the subway cars are being used to create artifi­cial reefs off the Atlantic coast from New Jersey to Florida.

Most of the region’s natural seabed is flat sand. Each sub­way car adds hundreds of square feet of hard surfaces for plank­ton, mollusks, and other tiny sea creatures to latch onto. After about five years under­water, a subway car is transformed (C).

Once established, the reef colonies attract small fish that feed on them—and larger fish, such as marlin and tuna, that feed on the small fish. The cars’ nooks and crannies also allow fish like sea bass to elude sharks and other big predators.

About 2,500 subway cars were dumped from 2007 to 2010, but they aren’t the only objects used. Arti­fi­cial reefs have also been created with tugboats, tanks, shipping con­tainers, and ships—including a U.S. Coast Guard cutter (D), shown here after 22 years on reef duty.