The Portage Fill Big Band has amassed quite a following over its 37 years of gigs on Vashon, in Ocean Shores, at the Quinault Lodge and elsewhere.

It’s also amassed a lot of paper.

Now, this home-grown band with a passion for the big sounds of jazz and swing is holding a fundraiser — one of its first — to come up with the money to digitally archive its reams of music.

Each chart, as the individual song sheets are called, averages two pages. And each member of the 18-piece band gets his or her own chart. Multiply those 18 charts by the 350 songs in its repertoire and by the number of pages for each chart, and Lou Engels, one of the group’s founders, estimates the band is lugging around nearly 7,000 sheets of paper to its performances.

If any of that music were to get lost or destroyed, he said, “It would be expensive to replace, if you even could replace it.”

So Saturday night, they’re asking fans to turn out for a performance at the Red Bike, with a cover charge of $5. It’ll be an opportunity not only to boogie to the band’s big sound, said Karen Eliason, the band’s baritone sax player, but also “contribute to keeping Vashon’s Portage Fill playing that music in the future.”

The Portage Fill is a beloved institution on the Island, drawing hundreds of Islanders to its outdoor concerts at Strawberry Festival and other events. And while its roots are modest — it started out as a quartet playing in Engels’ living room at his home at Portage — members know there’s something remarkable about the Portage Fill.

“It’s a rare community that has a band of this caliber,” Engels said.

The ensemble includes a few professionals — band director Tony Willing, trumpet player Richard Person and singers Maggie Laird — as well as several Islanders who play in other bands. Every seat is currently filled, and the joke among them is that someone has to die for a spot to open up.

Indeed, one performer did just that: Dick Thorlaksen, a legendary trombonist who performed with the band, played a remarkable riff at a concert at Chautauqua Elementary School in the late 1980s, sat down and died, Engels recalled.

“He just blew his socks off,” Engels said.

Engels, 72, is the only one of the founders still playing in the band. And last week, he took a break from his duties at Engels’ Repair & Towing to recall the band’s colorful history.

The Portage Fill has gotten some great gigs over the years, playing, for instance, at the Olympic Hotel for Charles Lovekin’s mother’s 90th birthday, he said. For years, they played New Year’s Eve at the Quinault Lodge on the Olympic Peninsula, while a friend of the band — Bob Haworth of Kingston Trio fame — played in the lounge next door.

These days, they practice about once a month at Williams Heating, a business trumpet player Dennis Williams owns.

Engels believes it’s the quality of the musicians as well as their rich repertoire that has made this group such an Island treasure. He rattled off the names of the jazz greats he loves — Duke Ellington, Bennie Goodman, Count Basie. Eliason agrees.

“The repertoire is fantastic. It’s an amazing period of time, and the music is interesting,” she said.

The Portage Fill will play an all-ages show from 8 to 11 p.m. Saturday at the Red Bike.