The regulation of flow of the Colorado River by Glen Canyon Dam began in 1963. This resulted in significant changes to the downstream ecosystem of the Colorado River in Grand Canyon, contributing to the initiation of the Glen Canyon Environmental Studies program in 1982, followed by establishment of the Glen Canyon Dam Adaptive Management Program in 1996. This report describes a water-temperature dataset collected through these programs for the reach of the Colorado River and selected tributaries between Glen Canyon Dam and Spencer Canyon (approximately 261 river miles) in northern Arizona from 1988 to 2005. The primary purposes of the report are to summarize the methods of data collection, processing, and editing; to present summary statistics; and to make the data described in the report available.