What Does Flood Stage Mean?
Every river gauge monitored by the National Weather Service has defined flood stages — specific water levels where flooding begins and gets progressively worse. Here's what each one means.
How Flood Stages Are Set
Flood stages are set by NWS hydrologists based on historical flooding, local topography, and what's actually near the river at each gauge — homes, roads, farmland, bridges. They're specific to each gauge location. A "minor flood" at one gauge might mean water on a farm road; at another, it means homes flooding.
Flood stages are measured in gage height (feet above a fixed reference point at the gauge), not feet of water depth.
The Four Flood Stages
Action Stage
The water level at which the NWS and local emergency managers start paying closer attention. It's a heads-up that flooding is possible if rain continues. Low-lying areas near the river may start getting wet. No formal NWS flood advisory is issued at this level, but it's time to monitor.
Minor Flood Stage
Water is out of the banks and causing some flooding. Low-lying roads near the river may be impassable. Agricultural land along the river floods. Some basements near the river may take on water. Inconvenient and potentially costly, but generally not life-threatening if you stay out of the water.
Moderate Flood Stage
Significant flooding. Roads are closed. Some homes and businesses near the river are flooded. Evacuations may be necessary in low-lying neighborhoods. This is where property damage gets serious and rescue operations may begin.
Major Flood Stage
Extensive flooding with significant threat to life and property. Large areas are inundated. Major roads and bridges may be impassable or structurally compromised. Widespread evacuations. This is a community-level emergency.
Important Things to Know
Every Gauge Is Different
"Minor flooding" means something different at every gauge. The NWS defines impacts specific to each location. Always check what the stage means for YOUR gauge.
Rate of Rise Matters
A river at 10 feet and rising 2 feet per hour is far more dangerous than the same river at 10 feet and holding steady. Watch the trend, not just the number.
Rivers Don't Crest Instantly
It can take hours or days for rain upstream to reach your gauge. A river can keep rising long after the rain stops in your area.
Turn Around, Don't Drown
Just 6 inches of moving water can knock you off your feet. 12 inches can carry away a small car. Never drive through flooded roads — you can't tell how deep the water is.
Monitor River Levels on Your Phone
StormCast monitors over 12,700 USGS river gauges and sends push notifications when water levels cross into a new flood category. You can track any gauge in the country and get alerts day or night.
