The Environmental Defense Fund celebrated a half-century of watchdog advocacy Saturday at a Huntington church, recounting past successes and bracing for challenges looming ahead.

The nonprofit’s roots reach back to 1966, when a handful of people gathered in the East Patchogue living room of Art Cooley, a Bellport High School teacher.

Concerned about Long Island’s declining osprey population, they decided to take action.

They sued the Suffolk County Mosquito Control Commission and notched their first victory: a judge’s order banning spraying of the insecticide DDT — which was harming the ospreys’ eggs. DDT would later be banned nationwide.

In 1967, the environmentalists signed papers at the Brookhaven National Laboratory, formally establishing the EDF. Their first office was an attic above the Stony Brook Post Office, with a staff of three.

The New York City-based organization now boasts more than 550 employees in more than 15 countries. It has offices in Washington, D.C., California, Massachusetts, Arkansas, Texas, Colorado, North Carolina, China, Europe and Mexico. Cooley still serves on the board of trustees.

The organization’s first half-century is dotted with major accomplishments, advocates say.

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In 1985, the EDF helped put an end to the use and sale of leaded gasoline, curbing a harmful pollutant. In 1991, it convinced McDonald’s to switch food packaging from plastic foam to recyclable materials. In 2004, FedEx reached an agreement with the EDF to use less-polluting hybrid trucks.

“The good citizens of Long Island deserve a lot of credit,” James Tripp, EDF senior counsel, said Saturday at the Unitarian Universalist Fellowship of Huntington.

State and local lawmakers presented the EDF and church with proclamations honoring their environmental work. About 80 people attended the event, which included a question-and-answer period.

It’s not just about the current generation, Huntington Town Councilwoman Susan Berland told the audience, but about “what we leave for our children.”

Tripp and Steven Hamburg, the EDF’s chief scientist, said the nonprofit uses scientists, economists, lawyers and others to tackle complex environmental problems. In recent years, the group has focused on decreasing carbon dioxide and methane emissions, promoting renewable energy and, locally, protecting the pine barrens and Carmans River watershed.

Speakers alluded to President-elect Donald Trump’s stance on the environment, including threatening to withdraw from the Paris Climate Agreement, eliminate the U.S. Environmental Protection Agency and boost coal and gas production.

EDF officials vowed to fight any rollbacks of environmental protections, but also urged those in attendance to remain positive.

“Who knows what’s going to happen?” Tripp said, noting that the organization is “still fighting the good fight, and we’ll continue to do it for another 50 years, at least.”