But the Indian government is cutting a shipping route through the shoals in what it is already touting as "India's Panama Canal". The finished canal, 167km long and 300m wide, will shorten the sailing time of ships from the Arabian Sea to the Bay of Bengal by more than 30 hours.
But environmentalists warn that the £300m project will be an ecological disaster, destroying precious coral reefs, and starving the endangered dugong, or sea cow. Local fishermen are protesting too, saying the project will kill fish stocks.
"An old wish is finally fulfilled," the Indian Prime Minister, Manmohan Singh, said at a ceremony to begin the Sethusamudram canal project in July.
A canal has been dreamt about since British colonial times. Unlike the Suez and Panama canals, which involved cutting through solid land, the Sethusamudram canal is a massive dredging operation. Around Adam's Bridge, the sea is shallow, varying from 10m deep to as little as 2.5m. India is using dredgers to cut a channel deep enough for ships.
The problem, Sanjeev Gopal of Greenpeace says, is the large amount of underwater sediment that will be disturbed by this dredging. He believes it will wreck coral reefs and affect the nearby Gulf of Mannar marine reserve. Home to more than 3,600 species, the Gulf of Mannar reserve has been designated as a world heritage site by Unesco.
Unlike a land canal, work on Sethusamudram will never stop. Underwater silting means the canal will have to be constantly dredged to keep it open. "[This] will spread the sediment far and wide," Mr Gopal says. "It will eventually smother the coral reef systems, and if they are smothered the reefs will collapse."
The Gulf of Mannar is renowned for its critically endangered dugongs. Mr Gopal says they too will be affected by Sethusamudram. "The sediment will make the water cloudy and prevent sunlight getting through," he says. "Sunlight is essential to the sea grass which the dugongs feed off."
As well as the dugongs, the Gulf of Mannar is home to sharks and sea snakes, and there have been sightings of humpback whales. Local environmental groups are mounting campaigns against the canal, but the Indian government insists Sethusamudram will not damage the marine life.
Sri Lankan environmentalists are furious that India did not even ask their government for its approval for a project that will have such a severe affect on Sri Lankan waters. But the Sri Lankan government, financially crippled by years of war with Tamil Tiger rebels, and coping with last year's tsunami disaster, is in no mood to argue with its far more powerful neighbour.
So far, the only government opposition has come from the state government of Tamil Nadu, within India. Environmentalists insist Sethusamudram is not only an environmental disaster, but a white elephant as well.
"When you talk about Panama and Suez, you're talking about saving 18 to 22 days of sailing," says Mr Gopal. "Sethusamudram will save one and a half days at best. Once you add in the cost of pilotage, a lot of commercial ships aren't going to use it."
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