In the particular case of the Glen Canyon Dam, the originally warm, sediment-filled, muddy water, instead runs cold and clear through the Grand Canyon, which has significant impacts on the downstream ecosystems.
In the particular case of the Glen Canyon Dam, the dams inherently change the water quality of the river downstream. Rather than warm, sediment-filled, muddy water, the water runs cold and clear through the Grand Canyon, which has significant impacts on the downstream ecosystems.