I thought I would expand "cooling rate modifier" to describe the physics behind it.
I imagine you could get that serious cooling if it were nice and windy and bone-dry, and you are dragging yourself up out of the river. Your skin would already be shut off from bloodflow, and the wind is sucking the water off.
In Palm Springs, they use evaporative cooling a great deal - and get tens of degrees of temperature reduction. I, though, would like to see some case studies first before I would say that it would happen. All I am willing to say right now is that it is possible.