Into her 80s, Elizabeth McQueen patrolled Queensbridge Park in Long Island City, Queens, wheeling her walker, a grandson or a great-grandchild at her side, eyes sweeping the walks and lawn. “If someone was barbecuing, she made sure they had garbage bags,” her grandson, Desmen Williams, said. “She had a bin of supplies. A rake if you needed to rake up. She made sure the fire barrels were out there, so you put coals in the barrel when you were done.”

The park is on the eastern bank of the East River, across from the Upper East Side of Manhattan, and Mrs. McQueen lived in the Queensbridge Houses, home to about 7,000 people, the largest public housing development in the country.

“We used to take the kids down to the park,” Dolores Chauncey, her friend and neighbor, said. “She’d say, ‘We’re on one side of the river and the millionaires were on the other, but we have the better view. We can lay in the park and watch the boats go by, and wait for the stars and moon to come out.’ And we did.”

Image Elizabeth McQueen leaned on officials to revamp Queensbridge Park, in Long Island City, whose esplanade reopened in summer 2014.

Mrs. Chauncey and Mrs. McQueen met about 40 years ago, another age in New York. The children splashed in a baby pool in the summertime, fished from the rocks when they got older, picnicked at all ages. But along the riverfront, the sea wall, built on a foundation of loose stone called riprap, was falling apart. To keep people away from the hazard, the parks department fenced off the area, including an esplanade. Decay marched on: One of two playgrounds was turned into a parking lot for people working on the Queensboro Bridge. The park house, with its concession stand and changing rooms for the wading pool, was left to the elements. And the pool was drained and filled in, visible only in the mind’s eye.