About the data
Every number on LakeLevelToday comes from the agency or operator that measures the lake, with its source and the time the source gives for it. Here's where each comes from and what it means.
Sources
| Source | What we use | How often it reports |
|---|---|---|
| U.S. Army Corps of Engineers | Corps lakes nationwide, plus lakes its districts monitor for other operators | Hourly or every 15 minutes |
| Bureau of Reclamation | Western reservoirs, including Lake Mead and Lake Powell | Daily |
| U.S. Geological Survey | Lake gauges across the country | Every 15 minutes |
| Texas Water Development Board | Texas reservoirs (Water Data for Texas) | Daily |
| California Department of Water Resources | California reservoirs (California Data Exchange Center) | Hourly or daily |
| U.S. Army Corps of Engineers, Detroit District, and NOAA's Great Lakes Environmental Research Laboratory | Great Lakes: lake-wide average levels (Corps) and surface water temperatures (NOAA) | Daily |
| Cube Hydro Carolinas | High Rock Lake, Tuckertown Reservoir and Badin Lake (North Carolina) | Hourly |
| Big Bear Municipal Water District | Big Bear Lake (California) | Weekly |
| Central Arizona Project | Lake Pleasant (Arizona) | Hourly |
| Central Nebraska Public Power and Irrigation District | Lake McConaughy (Nebraska) | Daily |
| U.S. Army Corps of Engineers, National Inventory of Dams | Dam names, owners, surface area and storage | Refreshed monthly |
How often pages update
We collect the newest readings every three hours. Lake pages also fetch each agency's daily values for the past year once a day, which picks up the corrections agencies make to provisional readings, sometimes weeks later. History older than that, and each lake's normals and records, are rebuilt once a month.
What the numbers mean
- Elevation is the water surface in feet above the vertical datum the agency uses (for example NGVD29 or NAVD88). Each page names the datum where the agency states it. Elevations from different datums can differ by several feet, so compare a lake only with itself.
- Full pool is the level the operator treats as full, usually the top of the conservation pool. Some operators change it with the season; then the page shows today's value. More about full pool.
- Percent full appears only where the agency publishes it, and each page says whose definition it is: Texas reports conservation storage, the Army Corps the share of its conservation pool, Reclamation storage against its maximum capacity, and the operators of Lake Pleasant and Lake McConaughy their own measures. Where an agency reports only elevation, we show feet above or below full pool and no percent.
- Normal is the median level for today's calendar date over the last 20 years of the lake's record.
- Records are the highest and lowest daily values in the agency's record. Where the record starts while the dam was new, records start the day the lake first filled, so the first filling doesn't count as a low. We call a record “all-time” only when it covers the lake's whole life; otherwise the page says when the record starts. Where another agency has a longer daily record for the same lake, and the two agree where they overlap, we use it for the earlier years and name it on the page.
- Daily values are the agency's own daily figure where it publishes one; otherwise the last reading of each day. We don't average readings ourselves. For the few lakes whose operator publishes no history, we keep one reading a day ourselves, starting October 2026.
How we check readings
Before saving a reading, we reject one that jumps far outside the lake's recorded range, or carries a time in the future or older than the reading we already have. A sudden jump bigger than the lake normally moves, or a steady move past the lake's record, waits for the next reading to confirm it. When an agency's feed is late, the page says “Data delayed” with the time of the last reading; after a week without readings, it stops showing a level and points to the agency.
Found an error?
Tell us. We fix data errors within a day.