Ice Climbing On Frozen Waterfalls

Grading in the Canadian Rockies, especially recently, focuses on the steepness of a pitch rather than the more subjective "feeling of difficulty" (mental aspects, e.g. protectability, exposure, commitment, etc.) or "technical difficulty" (e.g. chandeliers, bonding, etc.) during the first ascent. Hence the downgrading of several notorious routes, e.g. Sea of Vapours, which were in poor conditions during the first ascents.
A common use of the "+" designation is to indicate a higher level of technicality than is typical for the grade (e.g. chandeliers, poor bonding, etc.) that is consistent from year to year (i.e. Wicked Wanda, WI4+, has vicious mushrooms on an otherwise low-angled route, and these features always exist from year to year, probably due to the winds).
Finally, Canadian Rockies WI grading does NOT have anything to do with whether a climb is multi-pitch or not. Therefore, a 4-pitch WI5 is not granted WI6 just because it's long, and likewise a 4-pitch WI6 is not given WI7.
WI2 - low-angled (60 degree consistent ice), with good technique can be easily climbed with one ice axe. Grades beyond this generally require the use of two ice tools.