MIAMI (Reuters) - When people began dumping used tires in the ocean 40 years ago to create artificial reefs, they gave little thought to the potential environmental cost, or to how difficult it would be to pick them up.

A U.S. Navy Diver attached to Mobile Diving Salvage Unit (MDSU) 2 Det. 6 prepares a lift bag to salvage tires off the coast of Fort Lauderdale, Florida, June 4, 2007. MDSU 2 is conducting salvage operations in conjunction with U.S. Army Deep Sea Divers, and U.S. Coast Guard divers through the Innovative Readiness Training program. The goal of the salvage mission is to retrieve approximately 2 million tires. The tires were placed on the ocean floor in the 1970s to act as an artificial reef. However, coral would not stick to the rubber and the tires now present an environmental hazard. Salvage operations will continue for the next month then resume next year. REUTERS/Jack Georges/U.S. Navy photo/Handout

“It was one of those ideas that seemed good at the time,” said Jack Sobel, a senior scientist at The Ocean Conservancy, a Washington-based environmental group. “Now I think it’s pretty clear it was a bad idea.”

Now, local authorities are going after some 700,000 tires dumped off the coast of Fort Lauderdale, up the coast from Miami. A team of 40 divers from the U.S. Army, Navy and Coast Guard spent three weeks in June pulling up 10,373 sand-filled and slime-coated tires from the ocean floor.

Using the tire project as a salvage exercise, the military divers learned they could strap together 50 to 70 tires with wire cables and lift them to the surface with inflatable air bags, where a crane hauled the bundle from the water.

Millions of tires, usually bundled with nylon straps or steel cables, were cast into the sea off Australia, New Zealand, Malaysia and off the U.S. states of New York, New Jersey, North Carolina, California and Florida.

The idea was to provide habitat for fish while disposing of trash from the land, but in the rugged and corrosive environment of the ocean, nylon straps wore out and snapped, cables rusted, and tires broke free.

Thousands have been tossed up on U.S. shores, particularly during hurricanes. Tires dotted the sand as far as the eye could see along North Carolina’s Topsail Island after Hurricane Fran crashed the coast in 1996.

The tires dumped off Fort Lauderdale posed a particular threat. When they broke free they migrated shoreward and ran into a living reef tract, climbing up its slope and killing everything in their path.

“If we can keep the project going we think they can get all the tires and then the reef can recover,” said Ken Banks of Broward County’s Environmental Protection Department. “But the reef recovery will probably take decades.”

AIRCRAFT CARRIER

Officials said the Fort Lauderdale project drew together a host of government and military agencies to salvage the tires cheaply.

“If you have to pay to make them go away, it would have cost about $17 per tire. We got that down to about $2 per tire, in part because they are making other products out of them,” said William Nuckols, a project coordinator for Coastal America, a U.S. government agency.

The tires were trucked to a disposal plant in Georgia, where they were chipped into fuel for a waste recycling plant.

U.S. states no longer permit tire reefs. But Sobel said the entire concept of artificial reefs needs to be reexamined.

They have been created around the globe using all manner of material, from tires and concrete sewer pipes to discarded airplanes and ships. One of the largest, the rusting 880-foot (270-metre) U.S. aircraft carrier Oriskany, was sent to the bottom of the Gulf of Mexico last year.

They are promoted by local officials as tourist attractions and by fishing captains and scuba operators who say they create new habitats and nurseries for fish and other sea creatures.

But Sobel said there are big questions that need to be answered.

Do they damage natural habitats, as the tires did off Fort Lauderdale? Do they concentrate marine creatures and make it easier for fishers and divers to catch them, exacerbating an overfishing problem and causing lasting damage to fisheries?

Do they draw eggs and larvae that would otherwise settle in natural habitats?

“There’s little evidence that artificial reefs have a net benefit,” Sobel said.