They came by kayak, sailboat, jet ski, paddleboard, pontoon boat, by whatever watercraft they could to reach a Sunday afternoon beach party the likes of which they believe Sarasota has never before experienced.

On a Big Pass sandbar that at low tide stretched the equivalent of about three city blocks, 2,000 or more beachcombers — with dogs and children in tow — joined “Party on the Pass,” a rally to raise awareness for a cause launched by the environmental group Suncoast Waterkeeper and the Siesta Key group Save Our Siesta Sand.

The two groups have united to call for the U.S. Army Corps of Engineers to conduct a thorough environmental study of its plan for dredging Big Pass to replenish the beaches on Lido Key. The Corps' permit application is still pending before the Florida Department of Environmental Protection.

Justin Bloom, executive director of Suncoast Waterkeeper, said what is at stake is not just one dredging project but repeated dredging projects.

“Over a 50-year period, they could take enough sand to be equal to three times the volume of the Empire State Building,” Bloom said. “That's a massive amount.”

The Corps contends that dredging a shoal in Big Pass to renourish Lido Key to the north will not impact Siesta Key to the south.

Many Lido residents support the project, which would widen 1.56 miles of Lido beaches by an average of 176 feet.

Many Siesta residents counter that dredging will cause more wave action against their beaches and remove a source of sand that naturally replenishes their island's shores.

“We're not against beach renourishment and dredging per se,” Bloom said. “But it should be based on the best available science and adequate public input.”

Leaders of Sunday's demonstration want the Corps to conduct an “environmental impact study” rather than the narrower “environmental assessment” that the Corps prefers, Bloom said. “It's much broader and will include input by other agencies. It's a higher standard of review ... . We're just saying slow down. Let's use science. Let's use common sense.”

Rich Schineller, an advocate for both organizations, said one unknown is the “potential damage to marine life.”

Bloom said skeptics of the project worry that the dredged pass will become “a sand bank” that will be used not just for Lido but for renourishment projects throughout the region.

Jeanne Ezcurra of Save Our Siesta Sand said a Facebook.com page posted a few weeks ago started building support for the sand bar rally as hundreds upon hundreds promised to attend.

“This is awesome,” she said of the crowd that danced to a disc jockey's music, played Frisbee and relaxed on their boats and in beach chairs as they sipped beers and soda. “People have been very receptive.”

“Very receptive” is just the term that Eric Rubin used as well. Rubin took the opportunity to get signatures on petitions to put two state constitutional amendments on the 2016 ballot. One is to legalize medical marijuana and the other to allow residents to sell their excess solar power to their neighbors. He expected to have several hundred signatures before he headed back to shore.

“We're happy the community has shown their ability to appreciate Big Pass and hope that translates into support for preserving it,” Schineller said of the turnout. “It is certainly gratifying, it really is, to see people having a good time and being here for a common purpose.”