Work has begun on the largest dredging project in Boston Harbor’s history. The 3 and a half year, 350 million dollar “big dig” will widen and deepen the 7-mile long ship channel, allowing larger container cargo ships to deliver their goods to the Conley Container Terminal in Charlestown.

The first phase of the project began in September and involves digging a massive hole underwater in Boston’s inner harbor, near the confluence of the Chelsea and Mystic Rivers. Boston’s Port Director Lisa Wieland says this will permit ships to deliver oil, road salt and jet fuel for Logan Airport more efficiently, and it will also provide a place to put spoil from future dredging as the longer channels are expanded.

The second phase of the project, which will begin next spring, will deepen three shipping channels: the Outer Harbor Channel, the Main Shipping Channel and the Reserve Channel, according to a statement.

The US Army Corps of Engineers and Massachusetts Port Authority are coordinating the work, and the project's contractor is Great Lakes Dredge and Dock, which has 2 dredges on site working continuously. The project's cost will be shared — the state will pay $120 million, and the federal government will pick up the tab for the remaining $230 million. 

When complete, Boston will be able to service the largest cargo ships — some with 50 percent more containers — that have been passing from the Pacific to the Atlantic through the newly widened Panama Canal.

Four years ago, just five of the world’s 15 major shipping companies used Boston Harbor. Now 12 do, and the Harbor improvements will mean there will be no barriers to larger ships,