A year's worth of work cleaning the shores of Waimanalo Bay Recreation Area has been destroyed by inconsiderate beach users who are leaving behind fire pits with broken glass and trash, according to coordinators of the cleanups.

Some 15 blackened pits mar the white-sand beach that had undergone a transformation after volunteers with BEACH — Beach Environmental Awareness Campaign Hawaii — combed the Windward beach collecting bits of plastic and other debris brought in by the tides, said Suzanne Frazer, the organization's co-founder.

"After we got the beach really clean, we saw people camping there, walking, having weddings and picnics," Frazer said. "When the beach was covered in marine debris, it was deserted. Nobody uses a dirty beach."

Dean Otsuki, BEACH cofounder, said people are using pallets to build fires, leaving the nails in and then breaking their bottles, making the area unsafe for the barefooted beach users. Four-wheel vehicles bring the pallets to the beach, and the city needs to stop that, Otsuki said.

Ka Iwi shoreline had a similar problem and only concrete barriers could stop the illegal activity, he said.

"We need to keep people's vehicles off the beach so they can't bring the pallets," Otsuki said.