Since 2001, 714 retired New York City subway cars have been sunk off Delaware's coast to seed an artificial reef; within seven years the marine food per square foot there had increased 400 times - parade.com

An ambitious underwater experiment off Delaware’s coast has yielded striking results after transforming discarded New York City subway cars into an artificial reef. Since the project began in 2001, the submerged cars have created a thriving marine habitat, with researchers documenting a 400-fold increase in food availability per square foot within just seven years. The initiative highlights how repurposed urban infrastructure can support marine ecosystems, offering a rare success story in sustainable reef restoration. Environmental scientists and conservationists are now studying the reef’s rapid biological growth as a potential model for future coastal restoration projects.

Since 2001, 714 retired New York City subway cars have been sunk off Delaware's coast to seed an artificial reef; within seven years the marine food per square foot there had increased 400 times  parade.com