The waterbus between Dordrecht & Rotterdam Info
 

The highways in Holland are congested, and everyday there are plenty of
traffic jams, specially around Rotterdam. So they are now also using fast
Waterbuses to transport the people between city's not to far apart. They
are really fast, and as I always try to sail out of the way of traffic,
close as possible to the right side of the river, when they make a stop to
pick up passengers on the way, they sneak up behind you and use the horn
when they are around 10m (33 ft) away. They scared the hell out of me, I
believe they take pleasure in it. I always look back regularly for traffic,
but as the river is not a strait line many times you don't notice them.