The Saint Croix River rises from East Grand Lake at Forest City and flows southeasterly for 92 miles before emptying into Passamaquoddy Bay. Throughout its entire length, the river forms the easternmost part of the international boundary between the United States and Canada. For its last several miles, the river forms the boundary between Calais and St. Stephen, New Brunswick. The Saint Croix River is used by commercial fishermen from both nations.

Initial work on the river was completed in 1856. It involved construction of three piers to keep vessels away from a ledge opposite Mark Point Lighthouse, located about five miles downstream of Calais on the American side of the waterway.

The present project, completed in 1916, consists of:

• Repair of the piers.
• A 3.7-mile-long channel with varying dimensions extending from Hills Point at The Narrows to the Upper Steamboat Wharf near the International Bridge, which connects Calais and St. Stephen. From The Narrows to the Lower Steamboat Wharf at Calais, a distance of nearly two miles, the channel is 12 feet deep and 200 feet wide. From the Lower Steamboat Wharf to the public landing at St. Stephen, a distance of 1.5 miles, the channel is nine feet deep and 150 feet wide. From the public landing at Saint Stephen to the Upper Steamboat Wharf near the International Bridge, a distance of 2,000 feet, it is nine feet deep and 100 feet wide.