Drowning is possible even in low water levels - particularly in cold water with additional cold water shock and gasping.
If you rolled down the bank and your face hit the water you could still inhale a gulp of cold water leading to vocal
Here is a link to a medical article on the mechanism of drowning Drowning: Background, Etiology, Epidemiology
After initial breath holding, when the victim's airway lies below the liquid's surface, an involuntary period of laryngospasm is triggered by the presence of liquid in the oropharynx or larynx. At this time, the victim is unable to breathe in air, causing oxygen depletion and carbon dioxide retention. As the oxygen tension in blood drops further, laryngospasm releases, and the victim gasps, hyperventilates, possibly aspirating variable amounts of liquid. This leads to further hypoxemia.
IMO people underestimate the risks of especially cold but outdoor water in general.