A scheme to make the shallow strait between India and Sri Lanka navigable has upset environmentalists and the port of Colombo. To its supporters, it is a dream project, no less than the “Suez of the east”; to its opponents it is an environmental catastrophe. Either way, plans to dredge a channel in the seabed between India and Sri Lanka will be controversial, and could alter maritime and military operations in the Indian Ocean.

The $400m project, called the Sethusamudram Ship Canal, involves digging a 152km, 300m-wide channel through the Palk Strait, a shallow stretch of sea separating the south Indian peninsula and Sri Lanka. If it is created, it will carve out a continuous navigable sea route around India, and reduce the trip by a day for cargo ships that currently need to go around Sri Lanka.