How fast are private/motor boats allowed to go in the canals of Venice?

Question

I know there must be a limit because the city is supposed to be sinking, but I can't find anywhere that it gives any clue as to the maximum speed of motor boats (or if they are even allowed).

Answer 1

It varies, but only very slightly.  In some of the more modern, better defended areas it is 5 knots (approx. 5 mph or 8 kph) - but in the older more central areas, especially around the gondola bays, it is only 4 knots (approx. 4 mph or 7 kph)

I have visited nearly a dozen times, but never actually noticed the signs.  I only know because of my own curiosity, and asked a Gondaleer whilst being taxied about!