In the past year, Joel Meyerowitz has photographed serene marshlands and harsh, rocky promontories. He’s discovered tiny islands where crabs scuttle in and out of tidal pools, and found old-growth trees whose gnarled trunks are eloquent reminders of time’s passage. And in doing all of this, he hasn’t left the five boroughs of New York City.

The images are part of an ambitious project Meyerowitz has undertaken, with the blessing of New York City’s Parks Commission, to document a substantial portion of the city’s 29,000 acres of parkland over two years. So far, the project has taken him everywhere from tiny community playgrounds in south Brooklyn to an abandoned island off the Bronx—and to countless green spaces in between.

“It’s been a really wonderful gift to cover this ground and discover what appeals to me within it,” says Meyerowitz, who recently spent a day riding the length of the Bronx River in a canoe. Another aspect of the project has taken him to photograph all the large community swimming pools built by Robert Moses in the 1930s and 40s. “They’re amazing; really imposing,” he says.

All of this is a far cry from Meyerowitz’s last project, Aftermath, a visually and emotionally searing account of the clean-up and rescue operations at Ground Zero. In that case, the subject was restricted to sixteen square acres of lower Manhattan, and the only green to be found was the bright viridian of a crane repairman’s helmet. After Aftermath, “It feels good to be going out to the city’s furthest precincts, seeing all the natural abundance,” Meyerowitz says.

The idea for the parks project came from New York City Parks Commissioner Adrian Benepe, whom Meyerowitz has known since childhood. “I was photographing in Tuscany, and he called me and said, How would you like to take on the job of documenting 29,000 acres of New York City parks?” Meyerowitz recalls.

When Meyerowitz got back to New York, Benepe took him on an exploratory trip on the East River. They disembarked at North Brother Island, which served as a quarantine center for the contagiously sick during the Civil War era. “It’s really spooky when you come ashore,” Meyerowitz says of the abandoned island. “You climb up on an old rusting dock that’s covered in bird guano, then you’re faced with a wall of poison ivy 10 or 15 feet high. Through the woods you see these old ivy-covered buildings. Sometimes there’ll be a bench or a fire hydrant.” From that moment on, he was hooked.

Since both Aftermath and the parks project take New York as their subject, one wonders if Meyerowitz feels as though he’s becoming the city’s official visual archivist. Faced with that suggestion, he demurs with a laugh. “It goes deeper than that,” he says. “It’s about wanting to do work that’s socially useful. In this case, New York just happens to be the subject.”

Known for his elegant color images of Cape Cod and Tuscany, Meyerowitz has arrived at activism as a result of personal circumstance. “Ten years ago, my father developed Alzheimer’s,” he says. “I decided to make a film to help other families understand how this disease works, so I took my father on a road trip and made a very funny movie, which has now been seen by 40 million people. I realized it was a very useful thing to do. Then 9/11 happened, and I thought, as a New Yorker, what could I do to help?” When he found out that all photography had been banned at Ground Zero, he decided he'd create a visual archive of the site as a public service.

Now, photographing the city’s parks is giving Meyerowitz an opportunity to further his activism. If possible, he says, he’d like to extend the project by going in to city schools and conducting workshops for children, teaching them to document their local parks. “It would prepare the next generation of New Yorkers to be understanding and protective of their green belt environment,” he says.

In the meantime, he’s busy darting all over the five boroughs, capturing seasonal changes in his chosen locations. Whenever he makes an image, Meyerowitz takes a note of its GPS location: eventually, the Parks Commission will create a digital archive where users can click on a map and see images of the place they’ve selected.

So how do you document 29,000 acres of park space? “By not being literal,” Meyerowitz says. At first, he set about following in the footsteps of a 1930s WPA project that had faithfully documented every bridge, building, playground and gazebo. Then, standing in a wooded grove in Queens one day, he suddenly realized he was in the vestigial remains of the great Adirondack forests of the east coast. It was an epiphany. He started shooting in a more personal way, capturing the wild side of the parks.

Along the way there have been some nerve-wracking moments, like the one a few months ago when, photographing a carved rock in the northern reaches of Central Park, Meyerowitz surprised a trio in the middle of a drug deal. “I have a badge on a strap around my neck with a park seal, which lends me a little authority,” he says. “So when they shouted at me, I shouted back, saying, I’m making a picture for the parks, so just move along now!” He chuckles. “I don’t know what made me do that—I mean, the badge isn’t going to stop a bullet. When I told my wife about it she said, You idiot! You’re 69 years old. These guys aren’t playing games." He pauses, then adds: "But you know what? It worked.”

At the other end of Central Park, serenity awaited when Meyerowitz got the chance to photograph the Hallett Nature Sanctuary, a four-acre lakeside promontory that was closed to the public in 1934. For three months, Meyerowitz documented the sanctuary with an Olympus E-1 camera, compiling a 30-foot composite image that was auctioned at Christie's to benefit the Central Park Conservancy. "The image showed spring coming gradually to the Hallett; the camera did a beautiful job of capturing the seasons," he says.

A lake in Central Park, a swimming pool in Queens, a crumbling old hospital on North Brother Island. Ultimately, what brings all the images together is the photographer’s aesthetic, which is direct and uncompromising. “I could have skewed the entire project by shooting it only with glorious light,” says Meyerowitz, “but I wanted to show that these places can be beautiful on a rainy day or a sunny day.” It takes him back to his days as a young photographer in the 1960s, when he’d prowl the streets of New York trying to find transcendent moments in everyday interactions. “For me, an image has to have the electricity of discovery of the mundane," he says. "Something elbows itself into your consciousness, you have that momentary gasp of seeing something anew. That’s the thing I’m trying to photograph: that sense of wonder."