An attempt to save Florida's coral is wrecking the reef instead.
What seemed like a good plan at the time failed to take account of what sea water does to metal.
Diver Thomas Pennypacker is on a rescue mission off the coast of Fort Lauderdale.
He's saving a piece of Florida's natural coral reef from a massive 35-acre graveyard of old tyres.
It started as a way to get rid of the tyres clogging up landfills back in 1970 - up to two million tyres, bundled by metal clips, were dumped in the sea to create an artificial reef. The hope was that they would spur coral growth and attract fish – all of which is good for the environment.
It was a really good idea with a really bad outcome. The clips rusted away and the tyres broke free.