How We Measure Lake Levels
Where each number on this site comes from, how often it changes and what can go wrong.
Short answer: We read public gauges run by government agencies, store every reading and show the latest one with its source and time. We do not estimate or forecast levels.
The gauges
Each lake has a water-level sensor near the dam. In Texas, the Texas Water Development Board publishes a daily average for each reservoir, with storage and percent full. Elsewhere we use the US Geological Survey or the US Army Corps of Engineers, which publish readings every 15 minutes to an hour. The Great Lakes come from NOAA stations.
What we do with them
- Several times a day we download the newest readings and add them to the lake’s history.
- Changes over 24 hours, 7 days and 30 days are the difference between the latest reading and the reading closest to that time.
- “Same day in past years” uses the daily average of that date, or the nearest day with data within three days.
- Records skip the years when a new reservoir was first filling, so the lowest level is not the empty lake before the dam closed.
Limits
Recent readings from USGS and the Corps of Engineers are provisional and can be corrected later. A gauge can stop reporting; when the last reading is more than 48 hours old, the lake page says so in amber. For flood warnings, follow the National Weather Service.
Where this data comes from
See Sources for each agency, its coverage, update frequency and license.
Lake Levels Daily is an independent site, not affiliated with TWDB, LCRA, USACE, USGS, NOAA, TVA or any lake operator. Check official sources before making safety decisions.