As the United States grew divided over the Vietnam War, Mr. Seeger wrote “Waist Deep in the Big Muddy,” an antiwar song with the refrain “The big fool says to push on.” He performed the song during a taping of “The Smothers Brothers Comedy Hour” in September 1967, his return to network television, but it was cut before the show was broadcast. After the Smothers Brothers publicized the censorship, Mr. Seeger returned to perform the song for broadcast in February 1968.

Fighting for the Hudson River

During the late 1960s Mr. Seeger started an improbable project: a sailing ship that would crusade for cleaner water on the Hudson River. Between other benefit concerts he raised money to build the Clearwater, a 106-foot sloop, which was launched in June 1969 with a crew of musicians. The ship became a symbol and a rallying point for antipollution efforts and education.

In May 2009, after decades of litigation and environmental activism led by Mr. Seeger’s nonprofit environmental organization, Hudson River Sloop Clearwater, General Electric began dredging sediment containing PCBs it had dumped into the Hudson. Mr. Seeger and his wife also helped organize a yearly summer folk festival named after the Clearwater.

In the 1980s and ‘90s Mr. Seeger toured regularly with Arlo Guthrie, Woody’s son, and continued to lead singalongs and perform benefit concerts. Recognition and awards arrived. He was elected to the Songwriters Hall of Fame in 1972, and in 1993 he was given a lifetime achievement Grammy Award. In 1994 he received a Kennedy Center Honor and, from President Bill Clinton, the National Medal of Arts, America’s highest arts honor, awarded by the National Endowment for the Arts. In 1999 he traveled to Cuba to receive the Order of Félix Varela, Cuba’s highest cultural award, for his “humanistic and artistic work in defense of the environment and against racism.”

Mr. Seeger was inducted into the Rock and Roll Hall of Fame, in the category of early influences, in 1996. Arlo Guthrie, who paid tribute at the ceremony, mentioned that the Weavers’ hit “Goodnight, Irene” had reached No. 1, only to add, “I can’t think of a single event in Pete’s life that is probably less important to him.” Mr. Seeger made no acceptance speech, but he did lead a singalong of “Goodnight, Irene,” flanked by Stevie Wonder, David Byrne and members of the Jefferson Airplane.

Mr. Seeger won Grammy Awards for best traditional folk album in 1997, for the album “Pete” and, in 2009, for the album “At 89.” He won a Grammy in the children’s music category in 2011 for “Tomorrow’s Children.”