Data

How "Feet Down" is Computed

The USBR publishes two daily readings for a reservoir: the volume of water it holds ("af", acre-feet) and the water surface elevation ("fb", feet). This site works in elevation — "feet down" is how far the surface sits below the fullest the lake has ever been. The method:

• Each day's elevation is read off a single volume → elevation curve fit to the whole record: an isotonic fit — a curve constrained to only rise as the lake fills. A given volume always sits at the same elevation, so this curve is the real relationship; reading off it smooths the small day-to-day noise away for free.
• A handful of gross transcription errors — elevations off by many feet — are dropped before the curve is fit, and the occasional corrupt volume is repaired. The corrected data days are listed below.

Cle Elum Lake — Data Corrections

Cle Elum Lake's elevation record runs 1930-10-01 to 2026-08-20 — more than 35,000 daily readings.

The record starts on 1930-10-01, the first measured surface elevation. Earlier years had recorded volume but no measured elevation — rather than infer ~24 years of readings, they are simply not shown.

No days are excluded — every elevation reading sits within the normal noise of its rating.

Note — inferred elevations. 492 of Cle Elum Lake's days have no directly-measured surface elevation (gaps in the gauge record). On those days the "feet down" is inferred from the recorded volume through the rating curve — a modeled elevation, not a measured reading. The volume itself is measured throughout.

About the Raw Data

Highest / Lowest Lake Levels Per Year

Volume is in acre-feet.