I very much enjoy taking walks along the Rio Uruguay, or rather the River Uruguay, which is about 5 blocks from our apartment. There is a little paved trail that runs along the water just for such walks. The view is spectacular.
The first week we were here we went down to the "beach" to swim a bit. The beach wasn't exactly sandy. It was more muddy and pebbly, but we braved the mud and sand to take a dip in the water. Then, as we were getting out we realized there was a big sign with a picture of a swimmer with a giant red line through him/her. Of course--the universal "no swimming" sign. It figures.
No worries though; I've seen other people swimming in the river when I'm on my walks. The sign must be there, simply because there is no lifeguard, not because there are man-eating fish in the river. Or at least that's what I tell myself.