Joe Browder, environmental activist who helped lead efforts to preserve the Everglades in Florida. (Courtesy of Louise Dunlap ) (Courtesy of Louise Dunlap /Courtesy of Louise Dunlap )

Joe Browder, a onetime television reporter who became a crusading environmental activist in Florida, where he teamed with Marjory Stoneman Douglas and others to stop a large airport from being built in the Everglades, died Sept. 18 at his home in Fairhaven, Md. He was 78.

The cause was liver cancer, said his wife, Louise Dunlap, who ran a Washington-based consulting firm with her husband.

In the late 1960s, Mr. Browder gave up a budding career in TV news to become a full-time advocate for the fragile, often-misunderstood environment of South Florida.

One of his first successful fights was to preserve the waters of Biscayne Bay, within sight of downtown Miami, from development. He stood next to President Lyndon B. Johnson in October 1968 as the president signed a bill making the bay a national monument. (It is now a national park.)

Mr. Browder then turned his attention to a giant airport under construction in the Everglades, the vast swampy region covering hundreds of square miles in South Florida. Everglades National Park had been established in 1947, but not all of the land stretching across the southern Florida peninsula was protected.

In the late 1960s, commercial developers, with the support of many of Florida’s political leaders, began work on the airport in the middle of the Big Cypress Swamp, about 50 miles west of Miami. It was six miles from the edge of Everglades National Park.

The proposed Everglades Jetport would have been the world’s largest airport, five times the size of John F. Kennedy International Airport in New York. By 1970, a 10,500-foot-long runway had been built.

Mr. Browder helped galvanize opposition, citing an environmental impact study’s conclusion that the dredging and damming required for the airport would “inexorably destroy the south Florida ecosystem and thus the Everglades National Park.”

He also enlisted the support of Douglas, the venerable writer whose 1947 book, “The Everglades: River of Grass,” showed the region to be a delicate, complex ecological community rather than a watery wasteland.

Douglas did not consider herself an environmental activist until Mr. Browder persuaded her to take on a more visible role in 1969.

“Before Browder came along, she had been content with the semiprivate life of a writer,” University of Florida historian Jack E. Davis wrote in a 2009 biography of Douglas. “She was not the one who turned the Everglades into a cause, and she did not seek to join that cause.”

It was Mr. Browder who helped transform the dignified but feisty author into one of the country’s most renowned advocates of environmental preservation. Together, they founded Friends of the Everglades, which became an effective grass-roots lobbying organization.

Mr. Browder rallied an unlikely coalition to block the airport, including wildlife conservationists, Miccosukee and Seminole Indians and even “swamp rats” who relied on the Everglades for illegal poaching of alligators.

At public meetings, Mr. Browder confronted officeholders, business executives and aviation officials with scientific studies and a sharp tongue, outlining the devastation such a far-reaching project could have.

Advocates for property rights took up arms against him, distributing leaflets declaring him guilty of a crime that “equals any ever committed against mankind.” He received death threats. One elected official condemned Mr. Browder and another environmental activist, Nathaniel P. Reed, as “white radicals.”

“He was a born battler,” Reed told the Miami Herald, “he was a bulldog, he could step on toes and did step on toes.”

In the early 1970s, Mr. Browder testified at congressional hearings, and Reed became a top official in the Interior Department under President Richard M. Nixon. Ultimately, construction was halted on the Everglades Jetport after federal funding was withdrawn.

Mr. Browder drafted the bill that led to the establishment of the Big Cypress National Preserve in 1974, preventing the further development of hundreds of thousands of acres in South Florida.

More than 40 years later, the two-mile-long runway remains in place, a ghostly reminder of what might have been.

Joe Bartles Browder was born April 10, 1938, in Amarillo, Tex. During World War II, he moved with his family to Miami, where his father was stationed with the Army Air Forces.

He became fluent in Spanish, attended Cornell University and, by the early 1960s, was working as a reporter and producer with Miami’s NBC-TV affiliate. After leaving his television job, he was an official with the National Audubon Society in Florida and a founder of the Everglades Coalition, an advocacy group.

Mr. Browder settled in Washington in 1970 to work as conservation director for Friends of the Earth. He later helped found an environmental lobbying group before working at the Interior Department from 1977 to 1981, coordinating energy and land management programs.

Beginning in 1981, he ran an environmental consulting firm, Dunlap & Browder, with his wife. He worked on preservation efforts around the globe and was an adviser to businesses and public interest groups on climate change.

In recent years, he sought to limit damage to the Everglades from Florida’s sugar industry, and he was an advocate for the Everglades Headwaters National Wildlife Refuge and Conservation Area, a federally protected region in central Florida established in 2012. He also negotiated a settlement that led in 2015 to the opening of Maryland’s Franklin Point State Park on the western shore of the Chesapeake Bay.

His marriages to Joan Arrington Browder, an environmental scientist with the National Oceanic and Atmospheric Administration, and Marion Edey, an environmental activist, ended in divorce.

Survivors include his wife of 40 years, Louise Dunlap of Fairhaven; two sons from his first marriage, Ronald Browder of Jacksonville, Fla., and Monte Browder of Davie, Fla.; and four grandchildren.

When Mr. Browder was waging his battle against the Everglades Jetport, he knew he needed someone to stand above the fray as a symbol of moral courage. He turned to Douglas, the writer who coined the phrase “River of Grass” to describe the Everglades.

He was 31 and she was 79 when they met for tea at her fairy-tale cottage in the Coconut Grove neighborhood of Miami. Their partnership resulted in one of the most remarkable chapters in the nation’s history of environmental preservation.