Great Lakes other lakes as "the lower lakes", because they are farther south. Sailors of bulk freighters transferring cargoes from Lake Superior and northern Lake Michigan and Lake Huron to ports on Lake Erie or Ontario commonly refer to the latter as the lower lakes and Lakes Michigan, Huron, and Superior as the upper lakes. This corresponds to thinking of Lakes Erie and Ontario as "down south" and the others as "up north". Vessels sailing north on Lake Michigan are considered "upbound" even though they are sailing toward its effluent current. Lakes Huron and Michigan are sometimes considered a single lake, called
Great Lakes Waterway lake freighters to travel from the system's saltwater outlet to its far interior. The Waterway has larger locks and deeper drafts than the lower Seaway, limiting large freighters to the four lakes upstream of the Welland Canal and Lake Ontario and similarly restricting passage beyond the canal by larger ocean vessels. The two waterways are often jointly and simply referred to as the "St. Lawrence Seaway", since the Great Lakes, together with the St. Lawrence River, comprise a single navigable body of freshwater linking the Atlantic Ocean to the continental interior. Shipping channels separate upbound traffic from downbound traffic. The