Flood.global

River flood stages explained

River gauges tell you how high the water is now and how high forecasters expect it to get. The flood categories turn those numbers into what they mean for homes and roads.

Reviewed October 2026

Close-up of fast-moving, muddy brown floodwater
Fast-moving floodwater. Photo: Wolfgang Hasselmann on Unsplash

Stage and flow

A river gauge measures two things:

  • Stage is the height of the water surface, in feet, above a fixed reference point at that gauge. It isn't the water's depth, and a stage of 20 feet at one gauge says nothing about a stage of 20 feet at another.
  • Flow (or discharge) is how much water is passing the gauge, usually in cubic feet per second.

Because every gauge has its own reference point, what matters is how the stage compares with that gauge's own flood levels.

Flood categories

The National Weather Service sets these levels for each gauge, working with local officials based on what floods at each height.

Category What it means
Action stage The river is high enough that the NWS or local partners need to start preparing. Nothing is flooding yet.
Flood stage The level where rising water begins to threaten lives, property or commerce. Above it, the river is in minor flooding or worse.
Minor flooding Minimal or no property damage, but possibly some public threat, such as water over low roads or parks.
Moderate flooding Some structures and roads near the stream flood. Some people may need to evacuate or move property to higher ground.
Major flooding Extensive flooding of structures and roads. Significant evacuations are likely.
Record flooding The river reaches or passes the highest level ever measured at that gauge.

Each gauge's official page on water.noaa.gov lists what floods at specific heights there, such as "at 18 feet, River Road floods near the bridge." Those impact statements are the most useful part of a gauge page. Read them for gauges near you before a flood, while there's time to plan.

Observed and forecast levels

  • Observed is the latest measured stage, usually updated every 15 minutes to an hour.
  • Forecast is the level the National Weather Service expects in the coming days, issued for gauges where flooding is possible and for key gauges on larger rivers. Forecasts include rain that's expected to fall, so they can change quickly as storms develop.

A forecast crest is the highest level the river is expected to reach and when. If the forecast crest is in moderate or major flooding near you, plan to leave before the water gets there. Roads often flood before homes do.

Using the gauge finder

The flood lookup on this site lists river gauges near any U.S. address with each gauge's latest observed level, its forecast flood category when one is issued, and its flood stage. Each gauge links to its official NOAA page, which has the full forecast chart and impact statements.

A few things to keep in mind:

  • The nearest gauge may not be on your stream. Check that the gauge is on the river or creek that would actually flood your home.
  • Small creeks often have no gauge. Flash floods on small streams can rise in minutes with no gauge reading at all. That's what Flash Flood Warnings are for.
  • Gauges can fail. Floods and ice can damage gauges or give odd readings. If a reading looks wrong, trust official warnings and what you see.

Sources