In Venice, the canals are much like roads for the city, and have a lot more boat traffic on them than the peaceful tourist gondolas. Private, commercial and taxi boats are usually motorized which is great when you want to get somewhere a little quicker, but does make for a busy boatway.
Visitors should know what to expect. The canals aren't just a tourist attraction, they are a vital and active part of the Venice transit system. Too many boats? You can see the canals just as well from the many pedestrian pathways.
