Rolling your cursor over a dam symbol brings up a box with the current elevation of the water in the dam's reservoir, how that elevation relates to what is called for in the Water Control Diagram, and the amount of water flowing into and out of the reservoir.
Clicking on the dam symbol brings up more detailed water elevation and flow information, including how water levels relate to boat ramp elevations.
The large "cup" to the left (on the Willamette and Rogue diagrams) explains how close that system as a whole is to its Water Control Diagram.
The Corps of Engineers and other agencies collaborate on gathering and analyzing data regarding current and projected future reservoir and river level information.
This information is hosted on the Northwestern Division Water Management site.
In just a few minutes, this video highlights several key missions we perform on a daily basis in support of the Nation's economy, environment and quality of life: http://bit.ly/18PPHTq.