The Colorado River is a wonderful playground for Yuma County residents, out of state visitors and winter visitors. Unless your river activities take place strictly on the lower river below Imperial Dam, you may not realize that there is an ongoing daily change in the river water level above Imperial Dam. The reason for the fluctuations in the upper river is the change in irrigation demand from summer to winter crops. Generally, the highest flows, measured in cubic feet per second (CFS) take place in May, June and July. The lowest flows are in December and January.