HydroStatus

Data & methodology

Every number on this site traces to a public agency source. Build stamp: 2026-09-15T14:20:12Z.

Reservoir data

Colorado River system elevation, storage, inflow and release series come from the U.S. Bureau of Reclamation's Upper Colorado Basin hydrodata service (usbr.gov/uc/water/hydrodata), fetched nightly as published CSVs. USBR marks all values provisional and subject to revision; we re-fetch full series nightly, so upstream revisions flow through, and our raw-file archive preserves every version we have ever fetched. Lake Powell's daily record begins with Glen Canyon Dam's closure in 1963; Lake Mead's begins in 1935.

California reservoirs come from the state's California Data Exchange Center (CDEC), fetched nightly: daily reservoir elevation (sensor 6), storage (15), inflow (76) and outflow (23). CDEC's older digitized records carry occasional single-day errors (for example a lone 3,997-ft reading in a series that tops out near 1,084 ft), so we filter isolated spikes on the slowly-varying elevation and storage series — a value is dropped when it departs sharply from its neighbours and immediately reverts. Inflow and outflow, which spike legitimately during floods, are left unfiltered. Most California daily records begin in the 1980s or 1990s.

Derived numbers

Operating thresholds

Reference lines appear on charts only when the elevation is verified against a governing document, and every threshold in our database carries its source. Lake Powell: full pool 3,700 ft and minimum power pool 3,490 ft (USBR Glen Canyon Unit); the 3,525 ft target elevation (2019 Drought Response Operations Agreement, which defines it verbatim); dead pool 3,370 ft (USGS GCMRC extent dataset). Lake Mead: shortage-tier triggers at 1,075 / 1,050 / 1,025 ft (2007 Interim Guidelines Record of Decision, p. 38) and dead pool 895 ft (USBR FEIS Appendix B). Thresholds are stored as versioned data with effective dates because policy elevations change: the Mead tiers are recorded as in force through 2026, and when the post-2026 rules land this page will show what changed rather than silently editing numbers.

Weather

Observed temperatures come from NOAA GHCN-Daily stations: Page Municipal Airport (USW00003162, 1997–present, the only currently active station near the lake) and the discontinued Wahweap (USC00029114, 1961–2012), Page 4NNE coop (1957–2012) and Lees Ferry (1921–2012) stations for historical context. Forecasts are Open-Meteo model output, labeled as forecasts and fetched at build time. We do not mix modeled reanalysis into observed records.

Water temperature

There is no continuous official gauge for Lake Powell surface temperature — we verified this against the USGS instantaneous-values network (zero active water-temperature sites in the lake's bounding box). So the Lake Powell page shows a typical-surface-temperature climatology computed from the USGS Lake Powell limnology archive (1964–2022 data release, DOI 10.5066/P9ZIKVYW): monthly median and interquartile range of all top-1-meter temperature samples at the 28 monitoring stations within 15 km of Glen Canyon Dam or in Wahweap Bay, labeled as a historical average rather than a current reading. A satellite-estimated current surface temperature is a possible future addition and would be labeled as an estimate; we will never present modeled or estimated temperatures as measurements.

Planned

24-Month Study scenario projections (displayed as USBR's separate minimum / most probable / maximum scenarios, never as a statistical confidence band), CBRFC unregulated inflow outlooks, snowpack context, boat-ramp status (official NPS status kept separate from modeled usability), and a shoreline map built from USGS's Lake Powell extent polygons and topobathymetric DEM.