It's not realistic that one could cross a river and not have their temperature lowered, as long as they get in and get out within the rate of change. Once you get out of water, you'd still wet for a bit of time (maybe the duration is also based on the temperature around you?).

This would be helpful with BoP's hot spring water. Right now you still get the wet effect in the water , but it's hot spring water, so it should not be lowering your temperature. At least, not until you get out of the warm water and into the freezing mountain range (where hot springs are located). Thus, the player has to make the decision to warm up now and freeze later or keep being cold.