I've had mixed experience cycling along canals.... perhaps 8 years ago i decided to follow the canal from Coventry to Rugby. My only experience having been running along the Cov Canal.

For a few miles it was lovely on the towpath. Then the towpath just stopped and was basically a trod in the grass. Not ideal on my dad's road-bike which was too small for me anyway.

I did fall off at one point, and it was only the thickness of the vegetation which prevented me from ending up in the water.

By the time i got to Rugby i'd had enough and cycled to the station, and lumped the bike onto the first train home.