COLOMBO (Reuters) - A shipping canal that India plans to dig off its southern coast could have disastrous consequences for the marine and coastal ecosystems of neighboring Sri Lanka, environmentalists warned Monday.

Dredging in the shallow depths between India's southern tip and northern Sri Lanka could upset delicate ecosystems in the Gulf of Mannar Biosphere Reserve and Palk Bay and spell doom for fishermen from both countries, activists told a seminar held by the Green Movement of Sri Lanka.

"No-one in their right mind would dig a canal between India and Sri Lanka... The environmental impact in Sri Lanka has not even been studied," T. Mohan, an Indian environmental lawyer, said on the sidelines of the seminar. "We are talking about changes to the ecology ... sedimentation and risks to human lives if cyclones and tsunamis are to occur," he added.

This month the Indian cabinet approved a $550 million ship channel project to make it easier for ships to travel between the east and west coasts of the country. Only small fishing boats can pass through the Palk Strait at present.

Under the Sethusamudram Ship Channel Project, a channel will be dredged in the shallow portion of the sea off the southern tip of India so that vessels of up to 30,000 tonnes, including Indian Navy patrol vessels, will not have to circumnavigate Sri Lanka.

The Sri Lankan Minister for Ports and Aviation, Mangala Samaraweera, said this month the government was "concerned" about the Sethusamudram project, but did not elaborate.