So 1700ish road deaths a year, 25k serious injuries, set against:
(source)
223 deaths from drowning, most deaths happen in June, July, August, and 1/3 (78) were outdoors at beach, river, lake.
(Source)
After a cursory Google, I can find reference to one cold shock drowning in the UK. And it was a person entering the water quickly and without preparation. (Source)
We used to train for cold water shock at the outdoor centre – loch Tay never got above the ‘danger zone’ temperature, often way low. I’ve once had a child have a cold shock reaction jumping into the loch in March. I’ve had one staff member who capsized on an icy river Etive and reported real difficulty stopping herself from gulping in water involuntarily.
As with all risks, we need to put things into context and compare the real risks.