Floods

Flood Stages Explained: Action, Minor, Moderate, Major

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

Flood stages are water levels on a river gauge that the National Weather Service (NWS) uses to describe how serious flooding is at that spot. Above "flood stage" the river starts to affect lives, property or commerce. The NWS then sorts flooding into minor, moderate and major, with "action stage" as an early marker just below flood stage.

What are the official NWS flood categories?

The definitions below come from the NWS directive that sets its official water terminology (NWS Manual 10-950). They are measured in feet of gauge height at a specific gauge, not in depth of water on the ground.

Category	NWS definition (shortened)
Action stage	The level where action is taken to prepare for possible significant hydrologic activity, when reached by a rising stream, lake or reservoir
Flood stage	The level at which a rise in water begins to impact lives, property or commerce
Minor flooding	Minimal or no property damage, but possibly some public threat (for example, roads covered by water)
Moderate flooding	Some inundation of structures and roads near the stream, with evacuations of people and/or transfer of property to higher elevations
Major flooding	Extensive inundation of structures and roads, with significant evacuations of people and/or transfer of property to higher elevations
Record flooding	Flooding that equals or exceeds the highest stage or discharge observed at that site during the period of record

Minor flooding starts at flood stage. Moderate and major each start at their own higher stage.

What does action stage mean?

Action stage is not flooding. It is a level where the NWS or its partners start preparing. NOAA's National Water Prediction Service notes that the exact action is usually written in the local Weather Forecast Office's hydrologic services manual, and that action stage can be the same as the stage at which forecasts start being issued for a gauge.

Who sets the flood stages for a gauge?

Flood categories are defined separately for each NWS forecast point. The NWS directive explains that flooding at a given level is not the same everywhere along a river, because banks, channels and levees differ. So the category levels are tied to the most significant impacts somewhere in that stretch of river.

Local NWS offices review these levels over time. For example, the NWS office in Sioux Falls changed flood categories on several rivers after river surveys, elevation data, satellite images, records of past flood impacts and consultation with local and state emergency management officials. That is why two gauges with similar readings can be in different categories.

The directive also notes that not every forecast point has all three categories. A place protected by a permanent levee, for example, may not see impacts until moderate flooding. Some gauges have no flood categories at all, and NOAA labels those "flood category not defined".

Is flood stage the same as a record crest?

No. A crest is the highest level the river reaches during one high-water event. The record crest is the highest stage measured at that gauge since records began.

Flood stage is a fixed threshold chosen for its impacts. A record crest is a historical measurement. The NWS directive points out that the highest stage on record is not always above the major flood level. It can fall within any category, or even below flood stage, especially where the record is only a few years long.

It also helps to know that flood stage is not the same as bankfull stage. The NWS defines bankfull stage separately, as the level where the river starts to overflow its lowest natural bank in that stretch.

Where do I find official flood warnings?

Flood watches, warnings and forecasts come only from the National Weather Service and local authorities. You can find them at:

weather.gov, which shows active watches and warnings for your area;
water.noaa.gov, NOAA's National Water Prediction Service, which shows each forecast gauge with its flood categories and, where available, an official forecast.

Always follow the instructions of the NWS and your local emergency officials. The NWS runs the "Turn Around Don't Drown" campaign. Its guidance says it is never safe to drive or walk into flood waters, that 6 inches (15 cm) of fast-moving water can knock over an adult, and that you should never drive around barriers blocking a flooded road. Read the full NWS guidance on weather.gov.

For how flood forecasts are made, see NWS river forecasts explained. For record crests and peak flows, see annual peak flow and record crests. For gauge height itself, see gauge height vs streamflow.

Using this on Water Level Atlas

River pages linked to an NWS forecast point show a "Flood status" box with NOAA's current category, a table of the action, minor, moderate and major stages with how far today's gauge height is above or below each one, NOAA's official forecast where one exists, and NOAA's highest historic crests. Where gauge height is measured, a second chart draws the action and flood stages as dashed lines. A "NOAA" badge near the top shows the current category, and lake pages show it too where a NOAA gauge is linked. We never issue our own warnings; every flood box links to the official NOAA gauge page. See our methodology for details.