Waders of death?

[PAL]

Heat is lost more quickly in water than on land. Water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia. A water temperature of 10 °C (50 °F) often leads to death in one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. Water at a temperature of 26 °C (79 °F) will, after prolonged exposure, lead to hypothermia.

Thanks for doing the homework. Somewhere or other there's a temperature / survival time chart put together by the USCG. IIRC, it looks a lot like the data you cite.