The Colorado River leaves Glen Canyon Dam at fairly consistent and cold temperatures, generally from 8 - 10°C (46.5-50.5°F), though it may range from below 7° to 12 °C (44.5- 53.6 °F). Contrary to seasonal patterns, the warmest water is released in late fall and early winter, with release temperatures at their minimum in February and March. The river begins to equilibrate to ambient temperatures once it leaves the dam. Thus, the warm fall/winter releases soon begin to cool, while the cooler summer releases will warm.
Downstream warming is also influenced by the amount of discharge. A larger volume of water equilibrates with ambient temperatures more slowly than if releases are small, as a function of surface area to volume ratios. Much like the difference between a lake and a river. A river's volume responds more quickly to thermal warming or cooling than does the full volume of a deep lake or reservoir. This explains the high degree of warming that occurred in 2000, the summer of low steady discharges of 8,000 cfs. In contrast, the summers of 1997 and 1998 brought little warming to the river because of high sustained discharges of 18,000 to 27,000 cfs.
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