Walt Whitman hailed “Mannahatta” as “the place encircled by many swift tides and sparkling waters,” and Herman Melville wrote that even when New York City was belted by working wharves, deskbound crowds gravitated to “the extremest limit of the land” in order to “get just as nigh the water as they possibly can without falling in.”
About a century later, Cy Adler started his Great Saunter, an annual signature walk to promote his vision of a shoreline green ribbon encircling Manhattan, and to remind its residents that they inhabit an island. Mr. Adler, a mathematician and oceanographer by training, became the pied piper of the piers.
His group tours circumnavigating Manhattan and his books on the environment promoted the potential to transform the docks into parks, even before they had devolved into derelict victims of the high costs of labor and ground transportation and the shift to containerized cargo, which doomed shipping from Manhattan, where there was less storage space adjoining the piers.
Mr. Adler and others also started the Offshore Sea Development Corporation, which patented techniques to avert oil spills when unloading oil tankers, and to plant oyster beds more efficiently.
Shorewalkers, the irregular group of peregrinators that he founded in the early 1980s, announced that Mr. Adler died on Sept. 27 in a hospital in Manhattan. He was 91. His son David Adler said the cause was a stroke.
Mr. Adler’s Great Saunter, held on the first Saturday in May, has become a rite of spring for many.
It began in 1982 with an advertisement in The Village Voice and grew into an annual 32-mile, 10-hour hike through Hudson River, Riverside, East River and a dozen other littoral parks as well as barricaded, abandoned and bedraggled railroad yards and other tracts that, while not actually parks at the time, could have been linked in a verdant belt around Manhattan some day if he had mustered enough public support.
“The walker is the supreme conservator; he does not add pollution to the air or water, he does not waste natural resources, he destroys nothing,” Mr. Adler wrote in “Walking Manhattan’s Rim: The Great Saunter” (2003). The tours have since expanded into Brooklyn and the Bronx.
“Cy’s greatest legacy will be as an inspiration to civic engagement,” David Hogarty, the organization’s president, said in an email. “Cy was a great illustration of what it means to be undaunted.
“If he saw an issue like inaccessible waterfronts,” Mr. Hogarty continued, “Cy would just tackle it directly by literally getting boots on the ground to recognize the issue and then organizing to address it. He was unstoppable, always in forward motion.”
Cyrus Adler was born on Sept. 18, 1927, in Bensonhurst, Brooklyn, near Gravesend Bay, to immigrants from Romania, Harry and Sarah (Iolis) Adler. His father was a book salesman.
After serving in the Army as a military police officer from 1944 to 1946, he graduated from Brooklyn College with a bachelor of science degree and earned master’s degrees in oceanography and applied mathematics from New York University.
In 1952, while living on the Lower East Side as an N.Y.U. student, he grew restless for the sea and joined the crew of a Norwegian freighter bound for Manila. Returning to California on an American ship, he worked in the engine room.
His marriage to Patricia Murphy ended in divorce. In addition to their son David, he is survived by another son, Peter Anastasio; five grandchildren; and a brother, Leonard.
Mr. Adler taught physics and math for the City University of New York at its City College and Borough of Manhattan Community College campuses and at the State University of New York Maritime College, the New School, Long Island University and the Merchant Marine Academy. He also taught in the New York City public school system.
He addressed the risks that developing technology posed for the biosphere in another book, “Ecological Fantasies: Death From Falling Watermelons” (1973).
“In the world of the next 200 years, governments will have to work together to manage social institutions and natural resources,” he wrote in a 1973 Op-Ed article in The New York Times. “And those few persons given to thought will continue thinking, while the vast majority of mankind will continue to live intuitively — as has always been the case.”
Mr. Adler, whose Upper West Side apartment overlooked the Hudson River, retired as the president of Shorewalkers last year.
In 2006, he told Gothamist that his favorite shore walks were Inwood and Highbridge Parks in Upper Manhattan, that Inwood Hill Park was his favorite hideaway, and that someday he hoped the underappreciated waterfront would be transformed into a Harlem River park and a 330-mile Hudson River Trail to the river’s source, at Lake Tear of the Clouds in the Adirondacks.
He elaborated on this in 1997 in the book “Walking the Hudson, Batt to Bear (From the Battery to Bear Mountain),” which he wrote as Cy A Adler, with an introduction by the folk singer Pete Seeger. (Mr. Adler also wrote books under the name Peter Agnos.)
“Walking around the edge of a big city along an unknown path can change you, expand your horizons, knock you around for a while,” Mr. Adler wrote.
He told The Times in 1984: “You see things on these walks you wouldn’t see anywhere else in New York. We saw cows in Staten Island, oysters in the Bronx and pheasants above the George Washington Bridge. We saw dead chickens hanging from trees on the Harlem River that looked like they had been part of a voodoo sacrifice.”
“Should you get lost,” Mr. Adler added, “consider yourself lucky.”