SOURCES, CALCULATIONS & LIMITATIONS
A little context goes a long way.
Lake Levels is an independent, static guide to 30 Texas reservoirs for homeowners, boaters and anglers. It turns public observations into daily changes, seasonal comparisons and historical context. It is not affiliated with TWDB, TPWD or a reservoir operator.
Where the observations come from
The Texas Water Development Board's Water Data for Texas publishes historical CSV files for individual reservoirs. We use daily mean elevation, conservation storage, conservation capacity and the published percent full. Recent-conditions GeoJSON supplies reservoir reference coordinates and the current conservation pool elevation. Each lake page links directly to its inputs.
Elevations are in feet relative to the vertical datum shown on the source page. These are sea-level references, not depths; different gauges can use different datums. We retain the source datum label, including offsets, without converting it. Historical datum or pool changes can complicate long-term comparisons.
What “full” means
Percent full is conservation storage divided by conservation capacity, multiplied by 100. We prefer TWDB's published percentage, including its rounding; if absent, we calculate it from those two fields and cap it between 0 and 100%. Flood-pool storage is excluded. A reservoir can be 100% full and still rise above its conservation pool.
“Below normal” is the current conservation pool elevation minus the latest daily average elevation. This reference is not necessarily the operating target on a historical date. Capacity estimates can change following surveys or management decisions. Read TWDB's methodology.
Changes and missing readings
We subtract the reading exactly 1, 7 or 30 calendar days before the latest observation. The 24-hour change therefore compares daily averages, not two instantaneous measurements. An absent comparison date displays “Not available”; we do not substitute a nearby day or fill gaps.
The date of the latest reading appears prominently on every page. A warning appears if the latest reading is more than three days old at build time. A refresh fails if any lake is more than 14 days out of date, keeping a failed collection from replacing the deployed site. A failed deployment can still leave an older site online: always read the observation date.
Five-year charts and historical records
Snapshots retain the last five calendar years of available daily observations, relative to each lake's latest reading. The long chart shows this window. The seasonal chart overlays the latest twelve months and four preceding annual windows using matching calendar dates; February 29 is omitted where a shifted year has no matching date. Lines break at missing daily readings. The dashed conservation line is the current reference in both charts.
Records are calculated over the entire downloaded CSV before older daily rows are discarded. They are the minimum and maximum available observations, with the earliest date shown for ties. Older parts of the source record may be monthly rather than daily, so these are neither guaranteed all-time extremes nor instantaneous records. Each page gives its actual coverage dates and observation count.
Same-date comparisons use exact month/day matches within the retained five-year window. Their average uses only available prior-year matches, whose count is shown. It is a short comparison, not a climatic normal or a forecast.
The Texas overview
The hub's average is the arithmetic, unweighted mean of available percent-full readings for our 30 selected reservoirs. “Below 50%” counts only valid percentages. “Rising” counts positive exact seven-day changes. This selection is not all Texas reservoirs and its average is not the official statewide percentage, which uses storage volumes. Individual reading dates may differ.
Fishing and nearby lakes
Predominant species are extracted from the explicitly labeled list on each Texas Parks & Wildlife lake guide, when available. We link to the official guide for regulations and access, and make no claims about recent stockings or current catch rates. Nearby lakes are the three nearest in our selection by great-circle distance between TWDB reference coordinates, not road distance.
Updates and practical limits
A scheduled collection runs every six hours, with sequential requests, a short delay, timeouts and limited retries. TWDB may revise provisional observations. Site generation reads only a local JSON snapshot; it never requests data during a page visit. The initial snapshot is stored in the repository, while automated refreshes are deployed without creating data commits.
Water levels alone do not establish ramp access, safe navigation, swimming conditions, flood risk or fishing success. Check the reservoir operator and official emergency notices before making a trip. The site adds historical analysis to public observations; it cannot guarantee search placement or advertising approval.