New York City is famous for its towering skyscrapers and vibrant streets teeming with traffic, commerce, and cuisine. Turn back the clock a few centuries, and “the city that never sleeps” was known more for its marine biodiversity: a bustling island in a harbor teeming with life, including some of the world’s most extensive oyster reefs. Centuries of pollution despoiled New York Harbor, turning it into a virtual dead zone. But now, the most ambitious restoration project in any city on Earth aims to bring it back to life.

The fight for the harbor’s future is drawing together New Yorkers of all stripes. Architects, restaurateurs, high school students, and scientists are joining forces to bring back a creature that fits in the palm of a hand: the oyster. Why? Because this humble mollusk has a critical superpower—a single oyster can filter 12.5 gallons of dirty water a day.

They’re also being used to help ward off one of the major consequences of climate change. After Hurricane Sandy pummeled the city in 2012, landscape architect Kate Orff proposed a groundbreaking project called Living Breakwaters. The city is now building a reef-like structure off Staten Island that will dissipate the energy of incoming waves and help reduce storm-surge flooding. With assistance from the BOP, Orff’s design firm is augmenting its breakwaters with living oysters, which will strengthen the structure’s resiliency and naturally increase its height as sea levels rise.