Physical changes to the river below the dams have been profound. Flow in the Colorado River is snowmelt driven, and pre-dam flow patterns were dominated by large discharges from April through July, followed by low flows in late summer and fall. The river carried tremendous amounts of sediment from the highly erodible Colorado Plateau, and river temperatures were seasonally warm. Today, river flow is nearly decoupled from natural snowmelt, and peak discharges can occur in any month, often November to January. Daily changes in water releases as great as 566 cubic meters per second occur regularly for hydropower generation. Alluvial sediment, which once played a vital role in creating inchannel habitat, is now trapped behind the dams, and the waters below are clear and sediment-starved. Also, because water is released from the bottom waters of most reservoirs, water temperatures for hundreds of kilometers below the dams are very cold throughout the summer and relatively warm during the winter, a reversal of the natural seasonal cycle. (An exception is Flaming Gorge Reservoir on the Green River in the upper Colorado basin, where water is released from multiple reservoir layers.)