Florida officials have resumed raising some of the hundreds of thousands of tyres dumped off its shores decades ago during an unsuccessful attempt to create an artificial reef.
Between one and two million tyres were piled in the waters around Florida in the 1970s but coral and fish never took to them as hoped.
Now they are causing other problems, said Allison Schutes, manager of the Trash Free Seas programme at the Washington-based Ocean Conservancy.
"The ocean has ever-changing currents and storms, and they're moving around and smothering and killing natural coral," she said.
Military divers began the clean up in 2008, but the effort stalled as they were called away over the years to more urgent duties.
"We were fighting two wars, and there were natural disasters," said Pat Quinn, a Broward County natural resource specialist overseeing the new clean up. "When the earthquake happened in Haiti it was the same team who helped clear the port," he added referring to damaged piers vital for offloading relief supplies.
The Florida legislature had authorized $US2 million for the work and military divers tethered to the surface wearing heavy suits hauled out nearly 62,000 tyres.
Efforts began again last week, focused on the artificial Osborne Reef, a massive pile of about 700,000 tires dropped near Fort Lauderdale by dozens of boats in 1972, he said.
With a remaining $US1.6 million, Florida officials hope to raise another 90,000 tyres over the next two years.
They will be trucked across the state to Florida's west coast and burned for energy at a renewable waste plant near Tampa.
Still, more a half million will remain, partially buried on the sea floor.
Tyres have also been used in artificial reefs off New York, California, and North Carolina as well as Malaysia, Indonesia and Australia. In most cases, such efforts were halted after tires were found to be unstable.