If you’re lucky, usually in the spring, you might get to see the rare and amazing site of water falling down Grand Coulee Dam’s huge spillway about 300 feet to the river below.
Some years this doesn’t happen at all, which is the way most who “operate” the Columbia River prefer it.
Today, the rest of us get our wish. They’ve been “spilling” for the last two days, the result of too much runoff from the snow-packed mountains upstream, which is carefully and continuously measured to avoid flooding downstream.
The Bureau appears to be holding the level of Lake Roosevelt behind the dam at about 1267. Full is 1290 (feet above sea level, that is).
In the photo, less than 10 percent of the River’s flow is coming over the top. The rest of the 173,000 cubic feet per second is flowing through the dam, some of it making electricity.
You can check for yourself how much is currently spilling or flowing through and what the levels of the water are with is link.

Last Thursday, the official forecast was that the lake would come up over the next week to the mid 1270s. Here’s a graph of this years lake levels compared to last year’s.