Chances are you’ve seen this graphic at a CAP board meeting, in Know Your Water News or on social media. But do you have a good sense for what this graphic means and why CAP communicates it each month?

How do I know how much water is in the Colorado River System? The report shows the system content in terms of millions of acre-feet, as well as the date the report was created.

What do those buckets mean? The monthly Colorado River Water Supply Report provides a snapshot of storage in the Colorado River system’s key reservoirs – Lake Mead, Lake Powell and others in the Upper Basin (Flaming Gorge, Navajo, Blue Mesa, Fontenelle and Morrow Point). The buckets show each reservoir’s current elevation, representing the water stored throughout the system.

How do I read the table in the upper-left hand corner? This table shows the maximum storage capacity in each reservoir, the current amount of water in each reservoir and the change from the previous month. Green means elevation has gone up and red means elevation has gone down since last month.

Overall, the graphic tells the story of trends in the system’s water supply. Typically, we will see the Upper Basin filling in the summer from the runoff taking place April through July. Lake Powell elevation will peak in August or September and then decrease in the fall as it releases water to Lake Mead. In the Lower Basin, we’ll see Lake Mead decreasing in the summer as demand peaks and then recovering in the fall/winter.