Check this out, from my old swimming days growing up. A 25 meter pool (not yards, which is shorter) takes 66 laps to reach one mile. Keep in mind that is 66 laps with a turn and a WALL to push off of 66 times. I still swim 1-2 times a week to stay in shape and anything over 25-30 laps in an indoor 25 yard pool starts to add up. Straight shot, anything over 1-2 miles is enormous.

JBK and Troutly summed it up well. However, if you life depends on it, you can swim a lot farther than you would think, it's just an instict to survive.

The dude swimming the Miss. River is gonna have one raging case of jock itch......

By the way, if you thik 50* water is not very cold then you were on a 5 day heroin bender while you were swimming. I rafted in W. VA. in 42* water in a wetsuit (it was snowing outside the morning we left.....NOTE TO SELF.....Never go rafting on ice breaker weekend just to save a few 100 bucks) and I could not beleive how quickly that water chilled my body. Even skiing in early season mid 60's water is a breathtaker!!!!!!!