Low bridges (high water level) on the river cruises are a common occurrence (which is why the boats are constructed with a lowerable wheelhouse). It sometimes happens that even that is not sufficient and a river cruise has to be interrupted because there is not enough clearance. On the cruise I took in 2010, we made it under all the bridges, but the tour behind us could not and the passengers were taken by coach to the other side of the low bridge and were parceled out among 2 other boats that had space available that were farther along (mine was one). Another feature of the cruise boats is that they can be lowered in the water (take on ballast), even to the point where the water level is above the floor of the lower deck--the windows on that level are sealed to keep out the water (so I have been told--we didn't have to do it).

My 2010 cruise was with Avalon Waterways, which is now part of Globus. It was fabulous! I do have a few photos of the canals in Amsterdam: https://www.flickr.com/photos/8712554@N02/sets/72157625690807750/.