Lake levels and the conservation pool
A lake level looks simple: a number of feet above sea level, or a percent full. But "full" means different things to different people, and a number with no time or no reference point does not tell you much. A little vocabulary makes every lake page easier to read.
Conservation pool and flood pool
Most Texas reservoirs are built to hold water for people to use: drinking water, power, farms and recreation. The level the lake is designed to hold for those uses is called the conservation pool, and its top is often called full pool. Many lakes also have extra room above that line, the flood pool, that stays empty on purpose so the lake can catch flood water and release it slowly. Move the slider to see the two spaces.
An interactive drawing goes here in the app.
The Texas Water Development Board (TWDB) states that its percent full figure is based on conservation storage and conservation capacity, and does not account for storage in the flood pool. So the percent tells you about water-supply storage, not about how much of the flood space is in use.
Some lakes are not about water supply
TWDB notes that its statewide totals leave out flood control reservoirs, because they do not contribute to the water supply. Its example is Addicks Reservoir, a flood control lake that is not used for water supply and, under normal conditions, is empty. It also notes that Lake Amistad and Lake Falcon straddle the Texas-Mexico border, and that by treaty Texas holds rights to 56.2 percent of the conservation capacity of Amistad and 58.6 percent of Falcon. The two lakes' levels are physical; the share that counts for Texas is a legal one.
Why two sites show different numbers
TWDB says the current water level on its site should match the original source, such as the U.S. Geological Survey or the river authority that runs the gauge. Storage and surface area estimates can differ, mostly because organizations may use different elevation-area-capacity tables, called rating curves, and TWDB says it uses the best information available for things like dead pool and conservation pool elevations, which may not match between agencies. Historical levels can differ because they are adjusted to one common vertical reference.
What that means for you
- Compare a lake with itself over time, from the same source, before you compare two lakes.
- Treat a feet-from-full number as a guide to how the shoreline looks, not as a rating of the fishing.
- If a number looks wrong, look at the time it was measured. An old reading is a reading from the past, not a current level.
How TexCast shows it
On a lake page TexCast shows the level in feet, the conservation pool elevation when we have a sourced one, how many feet above or below it the lake is, and the percent of conservation storage, each with the time it was measured. Where we do not have a sourced conservation pool, we show the number and give no verdict, and where a reading is missing or old we say so and never show it as good.
Sources
- Water Data for Texas (TWDB): Statewide reservoirs, read 2026-10-08
- Water Data for Texas (TWDB): Reservoir FAQ, read 2026-10-08
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