This cross-sectional diagram shows the elevations and other details about the Great Lakes, and the length of flow of each of the components of the Seaway. The Seaway is 2756 kilometres long (as measured from the mouth of the St. Lawrence River to the head of the uppermost Great Lake, Lake Superior). Lake Superior is at an elevation of 183 metres, and has a depth of 406 metres. From it the Seaway passes through the St. Marys River to Lake Huron. Lake Huron has an elevation is 176.5 metres, and a depth of 229 metres. An offshoot of the Seaway would be going down nearby Lake Michigan. It elevation is also 176.5 metres, and it is 262 metres deep. From Lake Huron, the Seaway uses the St. Clair River, Lake St. Clair, and the Detroit River to get to Lake Erie. Lake Erie is the shallowest of the Great Lakes (only 64 metres deep). From Lake Erie to Lake Ontario, there is the steepest drop on the Seaway: a one-hundred metre drop from Lake Erie’s elevation of 174.l metres to Lake Ontario’s 74.8 metres. A lot of this is accounted for by Niagara Falls. Lake Ontario is 244 metres deep. On leaving Lake Ontario, all of the Seaway is in the waterbody specifically named St. Lawrence River. The lengths of the parts of the Seaway are as follows (with all figures being in kilometers): Lake Superior, 610; St. Mary’s River, 97; Lake Huron, 359; St. Clair River – Lake St. Clair – Detroit River, a total of 143 kilometres; Lake Erie, 380; Niagara area, 56; Lake Ontario, 365; St. Lawrence River to Montréal, 182; and downstream of Montréal to the Gulf of St. Lawrence, 564 kilometres.