How to Read River and Stream Flood Gauges

How to Read River and Stream Flood GaugesUSGS flood-stage colors explained — Normal, Action Stage, Minor, Moderate, Major Flood. Plus what stage, discharge, and percentile actually mean.USGS river and stream gauges measure the height and flow of water at a fixed point and report back every 15 minutes. Color tells you the current flood status; numbers tell you exactly where things stand.Status colors

Normal: Within historical normal range for this date.

Above Normal: Elevated but no flooding expected.

Action Stage: Monitor closely; low-lying areas may see impacts.

Minor Flood: Minor flooding (typical: roads, parking lots, fields).

Moderate Flood: Moderate flooding (homes, businesses, road closures).

Major Flood: Major flooding (significant damage, evacuations).

Stage vs discharge vs percentile

Stage: Height of the water, in feet above an arbitrary reference (NAVD88, ft AGL, or local datum). Easy to picture but not directly comparable between rivers.

Discharge: Volume of water flowing past, in cubic feet per second (cfs). Directly comparable across rivers — 10,000 cfs in a small creek is more dramatic than 10,000 cfs in the Mississippi.

Percentile: Where current flow ranks against the historical record for this date. "85th percentile" means 85% of recorded values for this day-of-year were lower. Useful for spotting drought (low percentile) and unusual high flows (high percentile).

Why this mattersFlash floods kill more Americans most years than tornadoes or hurricanes. Even small streams can rise from "normal" to "minor flood" within a couple of hours during heavy rain, and gauges give you real lead time to act.Part of the BloomWX learn library — beginner-friendly explainers covering every surface of the BloomWX weather dashboard. Open BloomWX to see live data for any U.S. county.