Slipped and fell into water in town. Cannot remember what happened. Struggling to swim. There is an old joke about most drowning victims being found with their fly undone. Alcohol near water is never a good idea.
Most paths along the Thames have no walls or fences, it's straight into the water.
There are also bridges with very low side walls. It's not too difficult to imagine someone losing their footing or tripping and going "overboard", especially at night on the way home from the pub...