The St Lawrence (nicknamed the Lake of the Thousand Islands is a river in east north America flowing north-east from LakeOntario and forming part of the border between Canada and the USA, to the Gulf of St Lawrence. Commercially it is one of the most important rivers in the world forming the eastern-most link of the St Lawrence Seaway. In different parts of its course it is known by different names. From the sea to LakeOntario it is called St Lawrence; between LakesOntario and Erie it is called Niagara river; between LakesErie and St Clair, Detroit river; between Lakes St. Clair and Huron, St Clair's river; between LakesHuron and Superior, St Mary's river or the Narrows, forming thus an uninterrupted waterway of upwards of 2000 miles. It receives the Ottawa, its principal auxiliary, at Montreal, as also the St Maurice, the Saguenay, and numerous other large rivers from the north.