How we calculate

Last updated: October 17, 2026

The reading and its time

Every lake level is the latest value the source reported, with the source's own time stamp, shown in Central time. Corps of Engineers gauges usually report every hour; the Texas Water Development Board publishes daily averages, so for Texas-only lakes the time is a date.

When a gauge goes quiet

If the Corps has not sent a new reading for 6 hours (48 hours for daily Texas values), the page switches to "Last reported level", the number turns gray and a notice gives the time of the last reading. We never show an old value as today's level.

Normal pool

Normal pool is the top of the conservation pool published by the Corps for each lake (for Lake Texana, the conservation pool elevation published by the Texas Water Development Board). Some lakes follow a seasonal guide curve, so their normal pool changes during the year; we use the value the Corps publishes for today.

Typical level for a date

For each day of the year we take every past year since 2016, find that year's middle value within three days of the date, and then take the middle value across the years. At least five years are needed. The current year is left out, so the comparison is with past years only.

Daily history

The charts and tables use one value per day: the hourly reading closest to noon, Central time. We remove obvious gauge errors of one to three days (a jump of more than 2 ft that comes straight back), and keep real floods and droughts. Elevations are in feet above the datum the agency uses (NGVD 29 for most lakes; two lakes use a project datum).

Percent full

We show a percentage only when the source publishes it: the Texas Water Development Board's percent of conservation storage for Texas lakes, and the Corps' percent of conservation pool where the district reports it. We do not compute our own.

Tides

Each town uses the nearest NOAA reference station within 15 km. Times and heights are NOAA's predictions, unchanged, in local time and in feet above mean lower low water (MLLW). The curve on each tide page is drawn between the predicted highs and lows with a smooth half-cosine; it is a picture to help read the table, not an extra prediction.

Weather

Wind and the 3-day forecast come from the National Weather Service forecast for the dam location, refreshed every 3 hours and shown as issued.