THE HUDSON RIVER extends from its headwaters in the Adirondack Mountains more than 300 miles south to its mouth in New York Harbor. The tides in the Atlantic Ocean raise its water levels four to six feet twice a day as saltwater is pushed north on a flood tide and freshwater, from the Hudson’s tributaries, flows south on an ebb. This brackish water is a perfect set- ting for eastern oysters, Crassostrea virginica, which once thrived in the intertidal and subtidal areas along the shorelines of the estuary from as far south as Sandy Hook to as far north as Ossining—more than 350 square miles.

According to Mark Kurlansky, whose book The Big Oyster catalogs their abundance in New York, about three thousand years ago the Indigenous Lenape people sustained them- selves with large amounts of oysters from these waters, leaving hundreds of shell middens behind with thousands of shells, some piled as much as four feet deep.

In 1609, when Henry Hudson entered the New York–New Jersey Harbor Estuary (also referred to as the Hudson Raritan Estuary and the Harbor Estuary), he had to navigate his ship around 220,000 acres of oyster reefs. The Hudson Raritan Estuary was once thought to be one of the most biologically productive, diverse, and dynamic environments on the planet, with the native oyster central to this thriving ecosystem.

Oysters are natural filter feeders and eat by pumping water through their gills, trapping food, nutrients, suspended sediments, and even chemical contaminants. As they do so, they help improve water quality and provide food and habitat to other animals. A single oyster is able to clean up to fifty gallons of water a day. Together, the original oyster population of the Harbor Estuary was capable of filtering all its water in a matter of days.

In the 1800s, the oyster not only populated New York’s waters, it also populated its streets. Kurlansky wrote that “by 1860, more than 12 million oysters were sold in New York markets annually. New York was the oyster-trading center of the world.” Oyster stands were scattered through- out the city, and, by his account, were “as commonplace as hotdog stands today.” Growing oysters in one of the greatest international port cities made New York the world’s oyster capital for a century. It is hard now to imagine the abundance of life that existed in the harbor.

Peter Malinowski, executive director of the Billion Oyster Project (BOP), which aims to restore the health of the estuary and its oyster population, described its once remarkable biological diversity: “When Europeans first arrived, they talked about there being so many seabirds that you couldn’t see the sky and so many fish you couldn’t see the surface of the water. That type of abundance doesn’t exist anywhere on earth anymore. In about one hundred years, New Yorkers had removed most of the wild oysters from the harbor and ate them, using the shells for building the roads and buildings that created New York City.”

The population of New York exploded in the nineteenth century, and by 1890 more than two and a half million people lived there. This growth had significant environmental effects on the landscape of the city and beyond, as the intensive use of natural resources and disposal of waste began to overwhelm the ecosystem. These effects were alarming to a growing number of early conservationists and activists. However, national policies worked against these efforts. Due to the Swamp Land Act of 1850, roughly 90 percent of New York City’s wetlands were filled, destroying natural watersheds and the important nurseries wetlands provide as habitat for thousands of species of plants and animals.

Unfortunately, the bay was not valued equally to the land, and raw sewage was discharged directly into it as early as the eighteenth century. By 1910, every day 600 million gallons of untreated sewage were dumped into New York- New Jersey Harbor Estuary. Water makes up more than 35 percent of the city and accounts for almost 166 square miles of the city’s land- scape. In the 1890s, scientists began making clear the connection between sewage, oysters, and outbreaks of typhoid, causing increasing concern about the connection of water pollution to human health. Commercial oyster beds throughout the estuary were gradually closed, and by 1927, as a result of increasing water pollution, development, and overharvesting, the last of the Raritan Bay beds was shut down, marking the end of oystering in New York City. Oysters became functionally extinct.

As Kurlansky wrote, New Yorkers “befouled the entire estuary of the Hudson River. The pollution also killed off clamming, lobstering, and both commercial and sportfishing. A New Yorker could no longer wade out or row out from shore and catch dinner. New York families could no longer earn a living harvesting the sea they lived next to.” Today, the New York–New Jersey Harbor is one of the most urban estuaries in the country.

BY THE LATE 1960s and early 1970s, environmental activists in New York — and across the United States — were becoming outraged by the state of their urban waters. New York’s Riverkeeper organization was formed in 1966, suing polluters to protect waterways. Famed folk musician Pete Seeger raised awareness aboard a 106-foot sloop that sailed the Hudson River. In 1970, an estimated one hundred thousand people celebrated the first Earth Day in New York, with the event raising awareness of environmental issues coast to coast.

In 1972, the Clean Water Act was passed. Today, because of pollution controls, New York City’s fourteen wastewater treatment plants together treat 1.3 billion gallons of wastewater daily. Industrial pollution has been dramatically curbed, garbage dumping has been banned, and the Superfund program of the US Environmental Protection Agency (EPA) is helping mitigate past industrial pollution in places like the Gowanus Canal. With these inputs greatly reduced, the natural processes of the estuary have a chance to flush pollution and restore biodiversity. Because New York has a combined sewage and water system, however, one-fourth of an inch of rain can be enough to overburden aging infrastructure and trigger a combined sewer overflow event. Every year, it dumps 27 billion gallons of combined sewage and stormwater into the Hudson. New York City is ranked first in the United States in raw sewage discharges. Not surprisingly, it is still considered unsafe to plunge into the Harbor Estuary, especially after a rainstorm.

Activists continue to work to protect the estuary from pollutants. Among advocacy groups is NY/NJ Baykeeper, whose founder, Andrew Willner, was a boatbuilder in Staten Island who saw firsthand the devastating effect that repeated oil spills had on the harbor during the 1990s. NY/NJ Baykeeper used Clean Water Act damages obtained from polluters to fund oyster restoration. With this funding, the group created some of the first oyster gardening projects in the bay, helping improve the natural ecology of the estuary and clean its waters. As James Lodge, a senior scientist for the Hudson River Foundation, said, “They started this amazing grassroots effort and inspired a lot of folks to think about what might be possible to do in a harbor like New York.” Meredith Comi, director of the NY/NJ Baykeeper Restoration Program, described her program’s work, saying that “we have always asked, ‘Why is this estuary forgotten?’ and felt that people shouldn’t give up on it, even if it is urban.”

Between 2004 and 2014, more than 140 organizations participated in the oyster gardening program. Resident stewards documented data on the health of oysters to inform future restoration projects that scaled up successes. Seventy-nine sites showed positive oyster growth outcomes. The number of oyster gardens, now called “oyster research stations,” grew to 215 by early 2019, and these sites continue to provide crucial monitoring data. As a keystone species upon which other species in the ecosystem depend, oysters serve as a litmus test for the health of the estuary.

Oysters have provided “a valuable face for the environment,” Comi explained. “They have been extremely useful in public education and promoting awareness, especially by getting people to participate in the health of their urban waters. It has changed awareness. Over the years, I’ve seen that more and more people care. All the educational programs that get people down to the water are starting to pay off.”’

THE EARLY SUCCESSES of oyster gardening inspired the long-term goal of growing one billion oysters in the New York-New Jersey Harbor Estuary, appropriately called the Billion Oyster Project (BOP). BOP was launched in 2014 by Peter Malinowski and Murray Fischer. After working at Hudson Riverkeeper, Fisher founded the Harbor School, a public high school on Governors Island. Malinowski was a teacher of aquaculture at the Harbor School who grew up on an oyster farm on Fishers Island on the eastern end of Long Island Sound. BOP leverages the public imagination that made the Mil- lion Trees Project in New York a success. As Malinowski noted, “One billion oysters is a big deal, it’s an ambitious goal, but it’s also attainable. It’s a tiny, tiny fraction of what used to be here.”

The project began at the Harbor School, and BOP’s reef construction and monitoring program is designed to integrate with curriculum. Students learn to build and operate boats, spawn and harvest oysters, design and create reef systems, and monitor restoration sites by diving in the city’s waters. BOP is currently the nursery for more than thirty oyster resto- ration projects in the Harbor Estuary. Since the project started, it has grown more than 47 million oysters and reclaimed and recycled 106 million pounds of oyster shells. BOP also works with approximately one hundred middle schools training math and science teachers to teach through the lens of oyster restoration. Classes steward oyster research stations, and their experiments are recorded in monitoring efforts.

Governors Island houses the BOP laboratory and is also the site where eight thousand pounds of shell per week are collected from approximately seventy restaurants. The shells are cured in a giant mound on the island and used as substrate for con- structed reef systems. Oysters attach themselves to these shells in tanks, or are grown in floating nurseries, and are then transplanted to reef systems in the harbor.

The public is engaged by volunteering to help assemble reef structures on Governors Island. They also help in BOP’s community reefs program in which people living in neighborhoods cut off from their shoreline monitor oyster reefs, therefore fostering a connection to the estuary and marine life. Even in the most polluted waters of the harbor, participants find bryozoans, polychaete worms, anemones, different species of tunicates, and blue crabs on the oyster cages. Malinowski is confident that these experiences shape the perspective of urbanites. “I think most New Yorkers don’t think about themselves living on the water, and the biggest realization for a lot of people is that there is life in New York’s Harbor,” he said. “Learning about specific species like seahorses and other animals gets people really excited.” This realization is critical to developing stewards of this immense urban estuary.

Growing public awareness has been paralleled by progress in policy. In 1998, state legislation designated 400 acres of the Hudson River as an estuarine sanctuary, recognizing its ecological value and protecting it as a research area. New York has begun taking steps to mitigate water pollution, required by a 2012 EPA consent order to comply with Clean Water Act standards. PlanNYC, New York’s 2007 Sustainability Plan, committed the city to a green infrastructure program that is now one of the largest in the United States. Under the de Blasio administration, many of these plans were built upon as OneNYC 2050. By 2020, DEP had constructed more than forty-five hundred green infrastructure projects. Water quality has improved since the mid-1980s. There is less garbage in the harbor and along the shoreline. Harbor waterways are now used for recreation through- out the year, and dissolved oxygen levels in the water, critical for fish survival, are increasing.

However, the Harbor Estuary has a long way to go before it will be as clean as the carefully monitored waters of a city like Copenhagen, where people regularly swim. Combined sewer overflow events still make contamination levels high in many parts of the estuary. Lodge described, “Although the Hudson River Park is defined as a marine sanctuary, no one treats it like one.” Malinowski illustrated this reality, saying, “The only way to really clean up the harbor is to stop polluting it. It shouldn’t be acceptable to be denied access to the greatest natural resource we have just because it’s contaminated with human waste. If that happened in Central Park, and the gates were closed because it was full of human shit and trash, it would stop immediately.”

Although oysters can help improve water quality in the harbor, perhaps their greatest impact is in generating public awareness and appreciation for the harbor as a natural area worth protecting. The impacts of water pollution are certainly evident to those who participate in oyster restoration programs. As Malinowski explained, “Oysters have an incredible ability to focus human enthusiasm. People get excited about putting oysters in the water, and when they realize that it’s not safe to be in because it rained yesterday, then the effects of pollution become real very fast.”

BOP works with a team of advocacy organizations, including NY/NJ Baykeeper and the Hudson River Foundation. Through their efforts, New Yorkers are increasingly seeing the return of the oyster to their waters. The reappearing oysters may not be safe for human consumption in the near future, but more importantly is that they are a key part of the estuary’s complex marine ecosystem. Comi has a deep appreciation for this natural resource after seeing the life in New York’s waters firsthand through her work at NY/NJ Baykeeper. She said, “In my time doing this, I have seen changes in the water quality. There are so many things living in these waters. In the summer, when we were monitoring oyster reefs in Raritan Bay, we saw humpback whales breaching with the New York skyline in the background! Not only are the oysters living in the parts of the estuary that we’re putting them in, they’re growing and reproducing. I see more and more species coming back.”

Excerpted from From the Ground Up: Local Efforts to Create Resilient Cities by Alison Sant. Reproduced by permission of Island Press, Washington, DC.