My parents live on a farm about 20 miles from here, and this same canal goes by their place. In my younger days, my friends and I would have our parents drop us off at Chestermere lake, and we would ride these things for about 3-5 hours on inner tubes. We'd usual get out at one of their parents farm. It was a fun way to travel. A few months ago, I was snowmobiling on them. Lots of fun to be had.
I think that the no swimming sign is simply a suggestion though. It's government brainwash. Pay your taxes, don't jaywalk, register your cars, eat your peas, yadda, yadda, yadda. What's next? Uniforms? No swimming in canals? Eating your peas? I certainly hope not.