As somebody who spent 42 years at sea and did countless drills and sea survival courses in that time I'm perfectly aware of the dangers of water, particularly cold water, which most are and how quickly it can disable and kill, even the well informed have fallen victim to it.
My main point was the police were wrong, in my humble opinion of course, to say with what appeared absolute certainty, she fell into the river. They have admitted there was no scuff or slip marks in the area of where her dog and phone was found to substansiate that theory. She appeared a sensible, fit woman used to the area and a swimmer. It was between 9 and 9:30am, light and with a fair few people in the vicinity at that time. I think their theory is she may have been trying to retrieve a tennis ball in the water which seems a big risk to take for something so trivial. Attempting to rescue her dog that had fallen in I could understand but apparently the dog was dry so that's unlikely. Her attire though if she had fallen in wouldn't have done her any favours and indeed hindered her efforts to get out. Given the small time frame, lack of CCTV evidence of her leaving by the areas covered by it I can again see why everything points to she fell in the river and sadly this may indeed prove to be true.
As for the canal analogy that isn't a great one. Most of the people who died in there were people on a night out, many separated from friends and under the influence of drink and/or other substances. Having walked sections of it the place has lots of dodgy terrain to navigate and that's in the daytime let alone night.
I hope the woman is found safe and well but sadly I fear this won't be the outcome.