Its boundary on the south is the parallel of latitude 49°, between the Pacific Ocean and Lake-of-the-Woods, then a chain of small lakes and rivers eastward to the mouth of Pigeon river on the north-west side of Lake Superior, and the Great Lakes with their connecting rivers to Cornwall, on the St Lawrence.
Comparatively few have simple outlines and an unbroken surface of water, the great majority running into long irregular bays and containing many islands, sometimes even thousands in number, as in Georgian Bay and Lake-of-the-Woods.
From this a canoe route over small rivers and lakes leads to the Lake-of-the-Woods, which lies between Ontario, Minnesota and Manitoba; and English and Albany rivers with various lakes carry the boundary to James Bay.
In northern Ontario lakes are innumerable and often very picturesque, forming favourite summer resorts, such as Lake Temagami, the Muskoka Lakes and Lake-of-the-Woods.
It includes Labrador, Ungava and most of Quebec on the east, northern Ontario on the south; and the western boundary runs from Lake-of-the-Woods north-west to the Arctic Ocean near the mouth of Mackenzie river.