Er oops, turns out I've got this wrong--I was relying on an old map which I've found to be usually more reliable than other maps, but it seems to be wrong here. Sorry about that.
I'd still quite like to hear on which section, e.g. between which entrances to the towpath, it happened.
Regents Canal goes to Limehouse Basin, where it meets the Thames and the Lea.
Edit: (source)