Capt Matt added a good point, however, you don't always mend up stream. You want to mend you excess line from faster moving water to slow moving water (across stream and occassionally downstream). If you put all the slack in the current it will pull the line out faster (more drag) than if you mend into teh slower water. Spring Creek is a great example of a body pf water that has various spreads of water about every 3 feet across teh stream. But most of the time the water is moving at a similar pace; this mend is done up stream.