Lake J.B. Thomas: 20.5% full as of 2026-09-18

Historical Data

Date Percent Full Mean Water Level
(ft) 		Reservoir Storage
(acre-ft) 		Conservation Storage
(acre-ft) 		Conservation Capacity
(acre-ft) 		Surface Area
(acres)
Most recent 2026-09-18 20.5 2,226.41 41,727 41,054 199,931 3,133
1 day prior 2026-09-17 20.6 2,226.45 41,852 41,179 199,931 3,137
2 days prior 2026-09-16 20.7 2,226.49 41,978 41,305 199,931 3,140
1 week prior 2026-09-11 21.0 2,226.70 42,639 41,966 199,931 3,160
1 month prior 2026-08-18 22.4 2,227.61 45,552 44,879 199,931 3,240
3 months prior 2026-06-18 24.9 2,229.07 50,383 49,710 199,931 3,385
6 months prior 2026-03-18 28.1 2,230.90 56,771 56,098 199,931 3,601
1 year prior 2025-09-18 34.7 2,234.37 70,067 69,394 199,931 4,061
*

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 2026-09-19 03:45 2,226.38 2,258.00 -31.62
1 hour prior 2026-09-19 02:45 2,226.38 2,258.00 -31.62
2 hours prior 2026-09-19 01:45 2,226.37 2,258.00 -31.63
6 hours prior 2026-09-18 21:45 2,226.39 2,258.00 -31.61
12 hours prior 2026-09-18 15:45 2,226.41 2,258.00 -31.59
24 hours prior 2026-09-18 03:45 2,226.41 2,258.00 -31.59
48 hours prior 2026-09-17 03:45 2,226.45 2,258.00 -31.55
*

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