Ice Climbing On Frozen Waterfalls

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.
WI3 - generally sustained in the 60-70 degree range with occasional near-vertical steps up to 4 metres (Cascade Waterfall, Banff; This House of Sky, Ghost River)