The St. Lawrence Seaway links central regions of North America to the Atlantic Ocean via the Great Lakes navigation system. Harmful non-indigenous aquatic invasive species have increasingly been introduced into the Great Lakes largely through the ballast water of inbound ships involved in international commerce. A variety of solutions have been proposed, with some advocating closure of the St. Lawrence Seaway to international shipping.Historically, it was an important artery linking grain surplus regions in Canada and the United States with international markets. However, during the past two decades the Seaway’s role has diminished as a grain transport artery. The objective of this paper is to develop an increased understanding of this decline and to offer thoughts regarding the likely reversal of the forces that may have caused it. Analysis indicates declining imports by selected world regions and domestic transportation legislation is central to the decline.