Just to clarify - wedding parties do not use narrow boats like this 

Obviously more than one type of boat uses this canal.
I took this pic in the dark, pointing and shooting blindly and using the flash.
None of the childer at that end of the boat were spooked anyway, they loved it.
I had an apprehensive girl either side of me, and Mrs M and Mr G had once each.  There were screams when they turned the light out (only briefly, but three times) but they were just for the thrill of the noise.