Environmentalists have dropped a lawsuit aimed at halting a federal beach-fortification project in Montauk.

Attorneys for Defend H20, a group based in Sag Harbor, on Thursday filed paperwork to end the federal case.

Defend H20 founder Kevin McAllister said Friday it didn’t make sense to continue fighting because the effort had failed to win an injunction stopping the $8.4 million project, which has been underway since November.

Early decisions by U.S. District Court Judge Arthur Spatt indicated he would ultimately rule against environmentalists, McAllister added.

“Our shot was trying to stop the work until the court considered the lawsuit on its merits, and that didn’t happen,” he said.

Defend H20 and several supporters filed the lawsuit in March in a bid to stop the U.S. Army Corps of Engineers from burying thousands of “geotextile” sandbags to form an artificial dune along 3,100 feet of chronically eroded ocean beach that superstorm Sandy had scoured in 2012.

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Army Corps officials said the project was designed to protect Montauk’s business district from storm surges while they crafted a more permanent plan to gird 83 miles of coastline from Fire Island to Montauk Point.

Defend H20 argued the wall of 1.7-ton sandbags could actually worsen erosion by reflecting the force of waves, and said officials at multiple levels of government ignored environmental concerns about the project.

More than a dozen protesters were arrested trying to stop the project with demonstrations on the beach in the fall.

McAllister said his group would continue scrutinizing efforts to artificially fortify the coastline and called the concerns in Montauk “a launching point for the larger conversation about coastal management.”

East Hampton Town officials, who backed the project, were named as defendants in the lawsuit along with the state, county and Army Corps.

Alex Walter, executive assistant to Town Supervisor Larry Cantwell, said Friday that town officials “appreciate the environmental groups’ passion.” He said they hope environmentalists push the federal government to replace the geotextile bags in a few years with a permanent design made entirely of sand.

An Army Corps contractor has placed about 8,000 bags of an estimated 11,000 planned for the beach, he said. The project, including the installation of fences, grass and walkways, could be completed by late March or April, he added.

Army Corps officials declined to comment on the case Friday.