Massachusetts Avenue transformed into a moving celebration on Sunday, filled with colorful costumes, booming brass bands, oversized puppets, and calls for social and environmental change.

Spectators lined the sidewalks from Davis Square to Harvard Square to watch the 2026 HONK! Parade, the finale of the three-day-long HONK! festival of activist bands, as it went through Somerville and Cambridge. Some captured the festival on their phones, while others watched it from folding chairs with family and friends. Children in colorful outfits watched as musicians played while walking down the street.

“It’s so fun to see so many different people playing so many different kinds of music,’’ said Cindy Manson, 59, of Arlington, who saw the parade in person for the first time, despite working on Massachusetts Avenue and hearing about the festival for years.

The annual parade brought together street bands, climate activists, social justice organizers, labor groups, immigrant communities, and other organizations, blending live music with messages about issues affecting their communities.

Joanne Sullivan, 79, volunteered at the festival for the first time, alongside her friend Charlo Maurer, 73, who has been involved with the festival for years. After learning about the festival from Maurer, Sullivan was captivated by the groups’ creativity and the different ways they express themselves.

“It’s really impressive that a lot of these bands come from other states and cities,’’ Sullivan said as she wore a HONK! sash across her body and walked the parade route.

During the parade, participants handed out fliers, spoke with spectators, and invited the crowd to join in demonstrations and chants.

Participants from DePAVE the Way, an initiative of Green & Open Somerville that organizes volunteers to remove unnecessary pavement from yards and driveways to make room for trees and other green spaces, staged a mock depaving demonstration. They used foam designed to resemble asphalt and imitation sledgehammers. The demonstration showed how transforming paved spaces could help address flooding, urban heat, and biodiversity loss.

“What we wanted to do is basically bring what we do in the yards and driveways out into the streetscape and show people this,’’ said Leigh Meunier, 44, a member of DePAVE the Way, wearing an “I’d depave that’’ shirt. “We wanted to invite the crowd right into depaving as much as we can.’’

Not every group needed a slogan to bring people together; for some, it was just hot dogs. Greg Nadeau, 59, of Somerville and the Somerville BBQ Coop, gave away 500 free hot dogs to parade spectators. The group began marching in HONK! 20 years ago, after forming as a group of parents with young children and gathering for Friday barbecues.

“We give out hot dogs, and most importantly, we give out serendipity,’’ Nadeau said, wearing a hot dog costume. “If you look at the faces of people, they’re filled with joy.’’

For Somerville resident Janet Taylor, 50, the parade was a chance to introduce her 7-year-old daughter, Mia, to its music and community spirit. Taylor said the event appeared larger this year, with more groups expressing political and social concerns. She also hoped the experience would inspire her son, who recently began learning saxophone.

“It’s really cool to see that grouped with music and how that can communicate to many generations, many age groups, and many people of different walks of life,’’ Taylor, who has attended the parade on and off since 2007, said.

For first-time parade-goers Andre Sloan, 26, and Paulina Hammond, 25, both of Somerville, the experience was emotional. The couple attended HONK! performances the previous year but watched the parade for the first time Sunday, walking alongside the bands from Davis Square to Harvard Square.

Hammond was struck by the creativity of the puppets, artwork, and dancing, while Sloan marveled at the musicians’ talent and the efforts behind the performances.

“I was tearing up at the beginning, just seeing all these people coming together,’’ Sloan said near Harvard Square. “So many people having something that they really felt passionate about.’’

Maurer, who has taken part in the parade as a participant or volunteer for 15 years and was a member of the Good Trouble Brass Band, one of the event’s founding groups, said she wishes more people knew about it.

“It’s too bad that more people don’t know about it,’’ Maurer said. “It’s such a happy time, and we don’t have that many parades that aren’t related to some holiday that you may not care that much about.’’

Aayushi Datta can be reached at aayushi.datta@globe.com.