Before the construction of Glen Canyon Dam, the Colorado River ran relatively warm and a muddy red. Beginning in the fall of 1991, releases from the dam have been modified from earlier practices to attempt to protect the environment of the Grand Canyon downstream.
Maximum releases have been set at 25,000 cfs, with hourly fluctuations restricted to a range of 5,000 to 8,000 cfs per hour. Simply stated, this means that while the release of water from Lake Powell can fluctuate from 5,000 to 25,000 cfs, there may not be more than an 8,000 cfs change from hour to hour. This restriction greatly reduces the abrupt flow changes which previously adversely affected downstream resources.
