 The multitude of rivers and lakes in the entire region is caused by the watersheds of the area being so young and in a state of sorting themselves out with the added effect of post-glacial rebound.Virtually all of Nunavut's rivers drain into the Hudson Bay or the Arctic Ocean.Arctic tundra (Köppen climate classification "ET") covers virtually all of Nunavut, the only exceptions being the area roughly between the Four Corners and Ennadai and Nueltin Lakes, where a marginal taiga forest exists, and small zones of permanent ice caps, found on some of the larger Arctic Islands (especially Baffin, Devon and Ellesmere) at sites having a relatively high elevation.