Lake J.B. Thomas: 23.1% full as of 2026-07-17

The elevation-storage rating curve used to produce the storage hydrograph is made of two segments: (1) the segment up to the conservation pool top (below the red line) is based on measured data, and (2) the segment in the flood pool (above the red line) is an extrapolation from the first segment and shouldn't be relied upon for flood storage information.

Historical Data

Date Percent Full Mean Water Level
(ft) 		Reservoir Storage
(acre-ft) 		Conservation Storage
(acre-ft) 		Conservation Capacity
(acre-ft) 		Surface Area
(acres)
Today 2026-07-17 23.1 2,228.04 46,953 46,280 199,931 3,278
Yesterday 2026-07-16 23.2 2,228.05 46,986 46,313 199,931 3,279
2 days ago 2026-07-15 23.2 2,228.07 47,051 46,378 199,931 3,281
1 week ago 2026-07-10 23.5 2,228.23 47,577 46,904 199,931 3,296
1 month ago 2026-06-17 24.9 2,229.12 50,553 49,880 199,931 3,391
3 months ago 2026-04-17 26.9 2,230.26 54,492 53,819 199,931 3,523
6 months ago 2026-01-17 29.7 2,231.81 60,104 59,431 199,931 3,724
1 year ago 2025-07-17 38.5 2,236.20 77,692 77,019 199,931 4,269
*

Percent Full is based on Conservation Storage and Conservation Capacity and doesn't account for storage in flood pool.

**

   Values above, including today's are averaged conditions. For near real-time instantaneous water level, see table below or the interactive map viewer.

Most Recent Instantaneous Water Level

Date/time Water Level
(ft) 		Conservation Pool Elevation
(ft) 		Height Above Conservation Pool
(ft)
Most recent 2026-07-17 10:45 2,228.09 2,258.00 -29.91
1 hour prior 2026-07-17 09:45 2,228.08 2,258.00 -29.92
2 hours prior 2026-07-17 08:45 2,228.07 2,258.00 -29.93
6 hours prior 2026-07-17 04:45 2,228.04 2,258.00 -29.96
12 hours prior 2026-07-16 22:45 2,228.04 2,258.00 -29.96
24 hours prior 2026-07-16 10:45 2,228.05 2,258.00 -29.95
48 hours prior 2026-07-15 10:45 2,228.07 2,258.00 -29.93
*

Data is provisional and subject to revision.

Additional Information

Impoundment date 1952-01-01
Vertical datum NGVD29
Dead pool elevation 2,200.00 ft above NGVD29
Service spillway crest elevation 2,258.00 ft above NGVD29
Emergency spillway crest elevation 2,264.00 ft above NGVD29
Emergency spillway crest elevation 2,267.00 ft above NGVD29
Maximum design elevation 2,275.00 ft above NGVD29
Top of dam elevation 2,280.00 ft above NGVD29
Conservation pool elevation 2,258.00 ft above NGVD29
Data download (CSV) period of record, last one year, last 30 days

Elevation-Area-Capacity Curves

1952-01-01 (source: USGS)
1999-11-01 (source: TWDB) : GIS Data
Data Source USGS:08118000
USGS Monitoring Location USGS:08118000

Lake Location