Flood stage and flood warning levels

World Water Levels shows the readings that agencies publish and the levels they set for a gauge. It does not issue flood warnings, does not repeat them and does not judge whether a flood is coming. The readings are provisional or unchecked raw data. For a flood warning, use the official service for your area, named at the end of this page.

Some agencies, such as the National Weather Service, tie flood levels to gauge heights. The Environment Agency describes its warnings by what forecasts show. The sections below say which agency does what, in the agency's own words.

A gauge height is counted from that gauge's own zero point, so a flood level of one gauge cannot be compared with the level of another.

• Gauge height and where the zero point comes from

The National Weather Service defines flood stage as "an established gage height for a given location above which a rise in water surface level begins to create a hazard to lives, property, or commerce". It says that its flood warnings are linked to flood stage, and that flood stage is not necessarily the same as bankfull stage.

The US Geological Survey adds that the National Weather Service uses gauge height numbers to tell the public about different levels of flooding hazard, and that the Survey shows those flood stages as lines on its gauge height graphs where they exist.

For many gauges the National Water Prediction Service publishes four levels: action stage, minor flood stage, moderate flood stage and major flood stage. Our place pages for United States gauges show them as that agency's levels, under its names. We do not restate what each one means; the National Weather Service does.

In England the Environment Agency provides three types of flood warning, in its own words: a flood alert, where flooding is possible; a flood warning, where flooding is expected; and a severe flood warning, where flooding could be a risk to life and significant disruption to communities. A severe flood warning can be issued before, during or after flooding.

The agency says it issues a flood alert when forecasts show that flooding may be possible, and a flood warning when forecasts show that flooding is expected. The typical range our pages show for an English gauge is the agency's range of usual levels, not a flood level.

The Environment Agency covers England only. Scotland, Wales and Northern Ireland have their own agencies.

Vigicrues, the French state's information service on the flood risk of the main rivers, shows a map of flood vigilance by stretch of river in four colours. Its legend says, here in translation:

• Red: risk of a major flood, a direct and widespread threat to the safety of people and property.
• Orange: risk of a flood with significant overflow, likely to have a significant effect on community life and on the safety of property and people.
• Yellow: risk of a flood with overflow and local damage, or of a fast and dangerous rise of the water, calling for particular vigilance, especially for exposed or seasonal activities.
• Green: no particular vigilance required.

The Czech Hydrometeorological Institute (CHMI) station data lists, for some gauges, the heights tied to up to three flood activity degrees, and an extreme flood level. Its data names the degrees stav bdělosti (vigilance), stav pohotovosti (readiness) and stav ohrožení (danger). Our place pages show them as CHMI's levels. We do not say what each degree means.

The readings of German federal waterways come from PEGELONLINE, the online service of the German waterways and shipping administration (WSV). For some of its gauges it publishes flood marks I, II and III, which our place pages show under those names. We do not say what each mark means.

Flood warnings in Germany come from the states. Their flood centres run a joint portal that shows the current flood situation at the gauges it includes across Germany, and the active state flood warnings.

For the Netherlands, Spain and Canada this page says nothing about flood levels. Use the official flood service of the country or region.

A place page says whether a reading is below, within or above the normal range for the date. That range is made from the same dates in past years. It is about what is usual for the time of year, not about damage. A reading above it has not necessarily reached a flood level. Only an agency's own level or warning says that.

• How we work out the normal range

For a flood warning, use the official service for your area. The services below are named here, not linked. Search for each name to reach its service.

• National Weather Service (United States)
• National Water Prediction Service (United States)
• Environment Agency, Check for flooding (England)
• Vigicrues (France)
• CHMI flood forecasting service (Czechia)
• German state flood centres (Germany)

The words quoted or translated above are the agencies' own. The pages they are taken from are named below. Search for each name to reach its page.

• National Weather Service glossary, Flood Stage
• US Geological Survey, Why we use gage height
• Environment Agency, Flood alerts and warnings

• 19 October 2026: First published.