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Statewide Texas reservoir monitoring, combining daily authoritative storage figures with real-time gage readings.
TWDB and USGS use unrelated identifiers and quite different names — the same lake is “Lake Lyndon B Johnson” in one system and “LCRA Lk LBJ nr Marble Falls, TX” in the other. Matching is therefore done on position: a USGS gage within 8 km of the TWDB gage location is accepted outright, and one between 8 and 30 km is accepted only if the names share a distinctive word.
That resolves 110 of the 122 reservoirs. The remaining 12 — including Amistad, Falcon, Texoma, and Toledo Bend — have no real-time USGS lake-elevation gage because they are operated by IBWC or USACE, which publish through separate systems. Those lakes show daily TWDB data only.
TWDB's record goes back decades — to 1940 for Lake Travis. Each lake page compares today against every other year on the same date, so you can tell whether a level is genuinely unusual or simply seasonal. Comparisons pool the three days either side of the date, because a single calendar day has only one reading per year and its extremes are noisy.
Percentiles use percent full, the only measure comparable across decades — elevation datums and reservoir capacities are periodically re-surveyed. Sedimentation means capacity itself changes over time, so cross-decade comparisons are close but not exact.
Drought conditions come from the US Drought Monitor, a joint product of the National Drought Mitigation Center, USDA and NOAA, published every Thursday. The statewide map has a county overlay, and each lake page shows conditions in the county containing its dam.
Counties are shaded by the worst category present anywhere within them, so a county shaded D3 is not necessarily in extreme drought throughout. The DSCI figure is the Drought Severity and Coverage Index, a 0–500 summary that rises with both how severe the drought is and how much of the area it covers.
Drought where a reservoir sits does not by itself explain its level. Most reservoirs are filled by a watershed reaching well beyond a single county, and releases are managed for supply and flood control, so treat this as context rather than cause.
Rainfall comes from CoCoRaHS volunteer observers rather than automated gauges. That is a deliberate choice: the obvious automated source, USGS precipitation, mixes stations reporting an interval total with stations reporting a running cumulative total, and the API does not reliably distinguish them — adding them up produced a 56-inch daily figure for one Texas site, which would be a world record. CoCoRaHS publishes a single already-totalled 24-hour reading per station.
The trade-off is timing: these are read by hand once each morning, so they are not real-time the way the lake and river gauges are. On lake pages, rainfall is measured near the dam, not across the watershed — a reservoir's catchment can extend hundreds of kilometres upstream, so local rain and reservoir inflow are related but far from the same thing.
Where available, lake pages show discharge at the nearest gaged river reaches above and below the dam. These gages are identified by walking the USGS hydrography network upstream and downstream from the dam, not by distance — a gage a few kilometres away is often on an entirely different river.
The distance from the dam is shown for each gage, because it determines how literally to read it: a release gage 2 km below the dam measures that dam's outflow, while one 60 km downstream has picked up tributaries along the way. The “gaged net” figure is not a closed water balance — ungaged tributaries, rain falling on the lake, evaporation, and direct withdrawals are all unmeasured, so it will not reconcile exactly with the change in storage.
GET /api/lakes — all reservoirs; supports ?basin= and ?status=GET /api/lakes/travis — one reservoir; supports ?range=30day|1year|all and ?gage=1All data is provisional and subject to revision by the originating agency. This site is not affiliated with TWDB, USGS, or any river authority, and must not be used for navigation, flood response, dam safety, or any other life-safety decision. For official flood information, consult the National Weather Service and your local river authority.