Mayor Mufi Hannemann yesterday recognized 11 community groups for their work to keep O'ahu's beaches clean.

In the past few months, hundreds of volunteers have collected thousands of pounds of marine debris, the mayor said.

In honor of that, Hannemann proclaimed August to be Beach Clean-Up Month, in a ceremony at Honolulu Hale.

"It is heartwarming that there are community groups who don't mind getting on their hands and knees, toiling in the hot sun to clean up our beaches," Hannemann said.

"We'd be hard-pressed if we had to do it just with city employees."

Among those recognized were volunteers with the Beach Environmental Awareness Campaign Hawai'i, a nonprofit group that stages seven to 10 large-scale beach cleanups every year and dozens of smaller ones.

Last Saturday, the group gathered 160 volunteers to clean up Kahuku beaches. They collected 15,000 pieces of marine debris, amounting to 4,150 pounds of trash and discarded items.

"It was our biggest cleanup ever, and I think it really shows the growing enthusiasm from the community," said Suzanne Frazer, co-founder of the organization.

Still, "more people need to be aware that the 'great Pacific garbage patch' exists, and it does bring a swirling mess of garbage to Hawai'i," Frazer said.

The group participates in frequent cleanups at Kamilo Beach on the southern tip of the Big Island, where "the density of the plastic in the water is nauseating," Frazer said.

Because plastic pieces are not biodegradable, they can cause serious harm to endangered marine animals when swallowed, she said.

Hannemann said he hopes that the hard work of volunteer groups will spur others in the community to join the effort to keep Hawai'i's beaches clean.

Also recognized yesterday were the Surfrider Foundation, Damien Memorial High School, the Honolulu Community Action Program, Queen's Day Treatment Services, Kanu Hawai'i, Kapa'a Hawai'i, Kappa Alpha Psi, Pearl Harbor, the Afloat Planning System Pacific and the Leahi Soccer Club.