Even more than for North America in general, the contrast between the modest extension of the Pacific catchment area and the great breadth of those of the Atlantic and Arctic Ocean is striking in Canada. While only small and non-navigable rivers belong to the former (with the exception of the lower Fraser), the San Lorenzo and the Lakes region partly mark the border with the United States, and also Hamilton (Labrador), which is the largest of the Atlantic rivers running entirely in British territory, divides its waters between Canada and Newfoundland.
The vast Hudson Bay (1.2 mil. Sq. Km.), Which penetrates almost 50 ° N. in the northern penepiano, collects almost all of its waters (with a basin, therefore, of about 3.9 mil. of sq. km.), and only a small part of them flows west to the Mackenzie, or to the East. in the open Atlantic. In reality, the bay represents only a fragment of this penepiano itself, submerged by postglacial transgression. The rivers that put their mouths run through the emerged part with centripetal direction, almost all marked by the same characters that give them the surface morphology: now widening into ponds or lake basins, now descending through rapids and waterfalls. With the indecision of the relief, which is the cause of the extreme indeterminacy of the watersheds, portages in this way they allowed the whites to penetrate, for hunting fur animals, even where the thick wooded covering would have made it particularly uncomfortable. Of these rivers the most important are the western ones, above all the Churchill (1800 km.) And the Nelson (700 km.; 2440 if joined to the two Saskatchewan; basin: 1.18 million sq. Km.) Great Slave Lake, the second emissary of Lake Winnipeg, into which Saskatchewan pours its waters, which descends from the Rocks and with its two long branches (North S., km.1300, South S., km.100) it crosses the prairie region by means of the Red River, which also leads into Lake Winnipeg, the Nelson system connects to Minnesota, and with it the course of the Mississippi; by means of the Winnipeg River, it connects to Lake Superior and with it to the South.
An intricate web of portages connects the Hudson Bay hydrographic domain with that of the Mackenzie, the only large river (6400 km.) completely Canadian. Resulting from the meeting of the Athabaska with the River of Peace, it conveys the waters of the three major lakes of northern Canada (Athabaska, Great Slave Lake and Great Bear Lake) and constitutes the largest river basin of the Dominion, but is of little importance as communication route, given the areas it crosses and the long period of winter frost. For the latter reason, the value of San Lorenzo is very low, which nevertheless represents, together with the Great Lakes, one of the most active communication routes in the world, and is, in any case, the real lung of Canada, of which it has largely determined the evolution, helping to preserve its own individuality in comparison with the neighboring states of New England. Even as a means of penetration alone, none of the Canadian rivers has the importance of the St. Lawrence, and neither is the influence of Columbia and Fraser comparable on the opposite side of the continental mass in enhancing the regions on the Pacific. In any case, the second, which runs entirely in Canadian territory, is the largest river in that catchment area and the only one that is worth remembering, both for navigation and for the abundance of fishing (salmon). As for the Yukon, the Alaskan border cuts its course in half. Its spring branches (Lewes, Pelly) are still imperfectly known; in the rest, though the river carves with deep cañones, the plateau that takes its name from it, allows easy access to the gold districts of its middle basin, where it begins to be navigable.
Canada is, as it is known, the richest region of lakes on earth. The variety corresponds to the number, even if in essence the origin is mainly related to the events of the glacial period. Wanting to put some order, it is worthwhile to distinguish the lakes belonging to the area of the shield, from those of the Rocky and prairies. The latter are already quite well identified by the fact that they correspond to closed basins and therefore have more or less pronounced saltiness (L. Johnston), the latter usually fill trunks of valleys (tectonic) and therefore almost all take on an elongated and narrow shape (Kootenay, Upper and Lower Arrow, L. Shuswap), as it is also, in part, in the eastern pleated zone (southern Quebec). Much greater, however, is the diversity of forms in the northern penepian, where lakes cover 20% of the total area and represent 57% of the length of all waterways. The extreme irregularity of the perimeter in the lake mirrors is partly a consequence of their instability, but partly corresponds to their different origin: where in relation to the contact between rocks of different resistance, where with the presence of areas already depressed in the pre-ice age and then over-excavated, where with the obstacle opposed by the moraine bands, where finally with a whole series of causes that can only be clarified with the detailed study of the individual areas. The following table summarizes the main characteristics of the most important Canadian lakes; the five major ones belonging to the San Lorenzo system are excluded.
Overall, continental waters cover just under 4% of the total area in Canada, 3.6% without taking into account the Laurentian estuary.