Using this site

How to Read a Water Level Atlas Lake or River Page

By the Water Level Atlas team · Last reviewed Oct 21, 2026

Every lake and river page puts the latest measured number at the top, then compares it with the past: recent changes, the normal range for today's date and the records. Further down are a chart, an email alert form, NOAA flood information and nearby places. This guide follows the order of the page.

The top data card on a lake page

The big number is the latest water surface elevation in feet, with metres below it. Next to it is the vertical datum, such as NAVD88 or NGVD29, when the operator publishes one (see vertical datums).

"Measured" gives the time of the reading in local time. The word "provisional" appears when the data has not yet been reviewed by the agency (see provisional vs approved data).

Badges sit under the number:

• Normal for the date (or Below normal, Much below normal, Above normal, Much above normal) compares today with the same date in past years. See normal for the date.
• Rising, Falling or Steady compares the latest reading with the reading about 6 hours earlier. For lake levels, a change of more than 0.05 ft (1.5 cm) counts as rising or falling.
• NOAA: ... shows the current National Weather Service flood category, where a NOAA gauge is linked. See flood stages explained.

The small boxes show, where available:

• vs full pool: how far above or below full pool the lake is. This only appears when the operator publishes a full-pool level on the same datum as the reading (see what is full pool).
• Conservation pool % full: from the operator's storage data (see reservoir storage and percent full).
• 24 hours, 7 days, 30 days: the change in feet. The 30-day box is left out when both full-pool boxes are shown.
• Normal for [date]: the median level for today's date in past years.

The top data card on a river page

The big number is flow in cubic feet per second (cfs), with m³/s and gauge height beside it. If a gauge measures only level, the big number is gauge height in feet. See what is cfs and gauge height vs streamflow.

River readings are marked provisional, because recent USGS data has not yet been approved. The badges work the same way as on lake pages. For flow, a change of more than 3% in about 6 hours counts as rising or falling. The small boxes show the 24-hour and 7-day change, the median "Normal for" today's date from USGS statistics, and water temperature, or "Not measured" where the gauge has no sensor.

What this means

A few short sentences built only from this place's own numbers, such as how today compares with the same date in past years and the record highs and lows.

The chart

The buttons above the chart switch the time range: 7D, 30D (the default), 1Y, 5Y and All. The solid line is the measured value. The shaded band is the normal range for each date, the middle 50% of past years (25th to 75th percentile). On lake pages a dashed line marks full pool where we can show it.

River pages linked to a NOAA forecast point can show NOAA's official forecast as a dashed line on the 7D and 30D views. See NWS river forecasts explained. Where gauge height is measured, a second chart shows the action and flood stages as dashed lines.

Email alerts

Under the chart is the form "Get an email when ... changes". Choose:

1. goes below or goes above, and type a level in feet (or a flow in cfs on flow gauges), or
2. (weekly summary) for a summary email on Mondays.

Enter your email and press Create alert. The alert starts once you click the link in our confirmation email. A level alert is sent when the value crosses your number in the direction you chose, at most once every 24 hours. Every email has a one-click unsubscribe link.

Further down a lake page

• Same date in past years: the level on today's date in earlier years, and the difference from today.
• Records & details: highest and lowest daily level with dates, when records begin, full pool (where shown above), storage, inflow and outflow in cfs, and water temperature, or "Not measured here". A link leads to the full history page with yearly highs and lows and monthly averages.
• Weather & wind: the NOAA National Weather Service forecast for the lake's location, about three days ahead.
• Flood information: NOAA's current status with a link to the official NOAA gauge page, where a NOAA gauge is linked.
• Nearby lakes with their distance and latest level.

Further down a river page

• Flood status: NOAA's current category, a table of the action, minor, moderate and major stages with how far today's reading is above or below each, NOAA's forecast peak where one exists, and NOAA's highest historic crests. If no NOAA forecast point is linked, the box says so and points to water.noaa.gov.
• Records: the highest annual peak flow and stage on record (see annual peak flow and record crests), the lowest daily value in the last 5 years, and the normal range for today's date with the number of years behind it. USGS calculates these day-of-year statistics from approved data only.
• Up & downstream: other gauges on the same river.
• Lakes nearby.

Using this on Water Level Atlas

Start with the big number and the badges, then use the chart's 1Y or 5Y view to see whether today is part of a longer trend. If you need to know when a level is crossed, set an email alert. Our methodology page lists every data source and explains how normal ranges are calculated, and the guides page has more explainers such as how river gauges work.