Sarnia is a city in Southwestern Ontario located on the eastern bank of the junction between the Upper and Lower Great Lakes where Lake Huron flows into the St. Clair River, which forms the Canada-United States border, directly across from Port Huron, Michigan.. It is the largest city on Lake Huron. The city's natural harbor first attracted the French explorer LaSalle, who named the site "The Rapids" when he had horses and men pull his forty-five-ton barque "Le Griffon" up the almost four-knot current of the St. Clair River in August 1679. The Blue Water Bridge links Sarnia and its neighboring village of Point Edward, Ontario to the city of Port Huron, Michigan in the United States. It spans the St. Clair River, which connects Lake Huron to Lake St. Clair. The bridge's original three-lane span, opened in 1938, was twinned on July 22, 1997, making the bridge the fourth busiest border crossing in Ontario. The Blue Water Bridge links Highway 402 with the American Interstate 94 and 69.Sarnia's grain elevator, the sixth largest currently operating in Canada, was built after the dredging of Sarnia Harbor in 1927. Within two years, grain shipments had become an important part of Sarnia's economy. The grain elevator rises above the harbor, and next to it is the slip for the numerous bulk carriers and other ships that are part of the shipping industry that includes vessels from all over the world. The waterway between Detroit and Sarnia is one of the world's busiest, with an average of 78,943,900 tons of shipping that annually traveled the river during the period 1993-2002.