The waters around New York once hosted 90,000 hectares of oyster reefs. They disappeared entirely due to pollution and overfishing but oyster reefs are a crucial ecosystem for several reasons. They soften the blow of large waves and surges, helping to protect the city from erosion and flooding. They filter pollutants out of the water, too. The Billion Oyster Project is restoring reefs with the help of local seafood lovers. It collects empty oyster shells from New York restaurants, implants them with oyster larvae and places them back in the water.