This is from the Blomfield Road and Maida Avenue part of Regent's Canal, in London, it appears. I was unsure where I was at the time but I found a point on the google map that looks approximately correct, based on where I remember going.
Also, the actual sign on the fence reads "no cycling," not "no dopes." I assume dopes are not welcome but bicycles are a more pressing problem in that specific zone.

Every location I visited during my Paris class trip was supposed to inspire me artistically. And then all I wanted to draw was some artificial, [presumably] trash-stuffed waterway in another city.