How Cold id cold?
Cold is what the Clyde is now . I swam in the Clyde and Gareloch as a
kid. At 10 years old that water was bitter.

Less than 25 Meters from a bank with the ability to get out is not bad.

Actually it does not even leave an argument, if you are reliably in
flat water, that is 20 + degrees and have a comfortable air temperature
you don't need any of this stuff. If you have a wind chill of - 20 as
posted earlier or any number of other safety issues a wet suit ( if
only a shorty ) is a good idea..
Alex