"Parks Canada was advising people to swim only in supervised areas"
That WAS a warning from August.....summertime in Canada.
I've seen many of waterspouts off the coast of Florida. They always are accompanied by heavy cloud cover over water. The film Carl showed was over land and was formed without a heavy cloud cover. However, towards the end of the film, the low and dark cloud cover became visible.
I think they captured a beautiful weather phenomena.