Data sources & methodology
Where the water levels come from
- U.S. Geological Survey (USGS) – Water Services instantaneous and daily values (reservoir and lake surface elevation).
- U.S. Army Corps of Engineers – Corps Water Management System (CWMS) data, including seasonal “top of conservation” levels.
- U.S. Bureau of Reclamation – RISE (Reclamation Information Sharing Environment) daily reservoir elevation.
- Texas Water Development Board – Water Data for Texas reservoir levels and percent full.
- Tennessee Valley Authority – observed lake levels and operating guides.
- California Department of Water Resources – California Data Exchange Center (CDEC).
- NOAA Tides & Currents – Great Lakes water levels (IGLD 1985).
How often it updates
The site collects new readings once a day and rebuilds every page. Some agencies publish hourly, others once a day, so the time of the latest reading is shown on every lake page.
Definitions
Full pool is the operator's normal maximum level (for example the top of the conservation or power pool). For reservoirs with a seasonal plan we use the summer maximum. The source of each full pool value is linked on the lake page.
Normal for the date is the median of official daily readings on the same calendar date (using a 7-day window) over the period shown on each page, usually 2006–2025. The normal range covers 8 out of 10 years (10th to 90th percentile). For Lake Cumberland, Dale Hollow Lake and Center Hill Lake we use the daily average published by the U.S. Army Corps of Engineers, Nashville District.
Target level is the operator's seasonal guide curve for that date: the Corps' top of conservation pool or TVA's flood guide / operating zone.
Limitations
Recent data are provisional and can be revised. Gauges sometimes go offline. Elevations are in feet above the vertical datum used by each agency. This site is for general information only and is not a substitute for official notices.