The Texas Water Development Board (TWDB) obtains lake levels from several partner organizations. These organizations maintain gauges at the reservoirs that automatically measure water surface elevation and transmit the data back to the TWDB. TWDB then collects data from these organizations via the internet.
Reservoir gauges provide near real-time measurements. This data is updated via the TWDB website throughout the day at six-hour intervals.
Using this data, the Water Board calculates averaged water level values for the day and displays this on their website.
The information provided on their website and these links is near real-time.
The graphs below are all mock-ups of data collected on 8/24/2015; for current data of reservoir levels click on the respective map below.