But dumping used tyres in the sea to make artificial coral reefs has been an environmental disaster.

This summer US military divers will start removing, one by one, some two million of them from the world's biggest 'tyre reef ', a mile off Fort Lauderdale, Florida, after they have been found to be killing coral, rather than creating it. Similar problems have been found all over the world.

Tyres, despite their humdrum appearance, present a peculiarly intractable problem. Leave them in piles and they can catch fire; dumps have burned uncontrollably for years. Shove them in the ground and they rise eerily to the surface. Yet over a billion of them require disposal worldwide every year.

So the idea of turning them into artificial coral reefs, mimicking the earth's richest underwater habitats, seemed an ideal solution. The idea was that corals would attach themselves to the rubber and grow, providing shelter for countless fish.

Fort Lauderdale was one of the first places to try it out. In 1972, over 100 private boats turned out to help.

Goodyear, which provided the tyres, even dropped a gold-painted one into the water from a blimp to launch the project ceremonially.

The idea quickly spread around the world. Malaysia and Indonesia were among developing countries that launched huge programmes;

by 1995 there were 67 tyre reefs off the Malaysian coast alone.

"The really good idea was to provide habitat for marine critters so we could double or triple marine life in the area, " says Professor Ray McAllister of Florida Atlantic University, one of the organisers of the Project.

"It just didn't work that way. I look back now and see it was a bad idea."

Corals obstinately refused to grow on the surface of the tyres, and few fish took shelter among them. The only life that seemed attracted to them were 'weedy' species like sponges and stinging hydroids.

Worse the tyres eventually broke free of their chains and slamming into real coral reefs, seriously damaging them. Many settled on the corals, doing even more damage.

William Nuckols, co-ordinator for Coastal America which is helping to organise the clean-up, describes them as "a constantly killing coraldestruction machine".

It is likely to take three years and at least $40m to remove the tyres, in Florida alone. "It's easy to throw something into the water, " says Keith Mills of the Florida Fish and Wildlife Conservation Commission. "It is very expensive to remove it."

They tyres are also coming back to land. In 1993 a storm dumped half a million tyres on North Carolina beaches. James Francesconi, North Carolina's artificial reef coordinator, says: "I encourage no-one else to put another piece of freaking rubber in the ocean again".