CFS stands for cubic feet per second — the standard US unit of streamflow measuring the volume of water passing a point each second. 1 CFS equals about 449 gallons per second.

Frequently Asked Questions

Q: What is a good CFS for kayaking?

It depends entirely on the river and the section. Class II–III whitewater typically runs well between the 25th and 75th percentile. Very low flows (below 10th percentile) may mean too shallow to paddle. Very high flows (above 95th percentile) are often dangerous and may require expert-level skills.

Common questions about stream gauge data, river levels, and how to use StreamFlowData.com.

How often is the data updated?

Current readings are refreshed hourly from the USGS NWIS instantaneous values (IV) service. StreamFlowData.com caches these readings for one hour using Redis, so the data you see is at most about an hour old. The "updated X ago" label on each station page shows exactly how fresh the data is.

What does CFS mean?

CFS stands for cubic feet per second — the standard US unit of streamflow. It measures the volume of water flowing past a fixed point every second. One CFS equals roughly 449 gallons per second. A small stream might flow at 10 CFS; the Mississippi at St. Louis averages about 175,000 CFS. See the glossary for a full definition.

What is percentile rank and why does it matter?

Percentile rank compares today's streamflow to the historical record for the same calendar date. A rank of 50 means today's flow is right at the median — totally normal for this time of year. A rank of 5 means the river is extremely low (only 5% of historical years had lower flow on this date). A rank of 95 means it's very high. Percentile rank is more meaningful than the raw CFS number because it accounts for seasonal variation.

What is a good CFS for kayaking or rafting?

It depends entirely on the specific river and section. Generally, flows in the 25th–75th percentile range (labeled "Normal") represent typical paddling conditions. Very low flows (below the 10th percentile, labeled "Very Low") often mean shallow, rocky conditions. Very high flows (above the 95th percentile) may be dangerous for intermediate paddlers. Always check local paddling resources and never paddle beyond your skill level.

What CFS is good for trout fishing?

Trout fishing generally improves at moderate, stable flows — often the 25th to 75th percentile. Very high flows wash out holding areas and make wading dangerous. Very low flows concentrate fish but can stress them, and many rivers have voluntary closures during extreme low-flow conditions. Local fishing guides and fly shops are the best source of current conditions for a specific stretch.

What is flood stage and when is it dangerous?

Flood stage is the gage height at which a river begins to overflow its banks and cause damage. There are four thresholds: Action Stage (prepare, monitor), Flood Stage (minor property damage), Moderate Flood Stage (significant inundation), and Major Flood Stage (severe, life-threatening). The flood status page shows all gauges currently at or above flood stage.

Why does river flow fluctuate so much?

Rivers fluctuate due to precipitation (rain falling in the watershed), snowmelt (spring runoff can cause dramatic seasonal peaks), dam releases (regulated rivers can change rapidly based on operational decisions), and evapotranspiration (summer heat reduces runoff). Some rivers are highly variable — rising and falling within hours after storms. Others, especially those fed by large groundwater systems or regulated by dams, have very steady flows.

Why is gage height different from depth?

Gage height (also called stage) is the water surface elevation measured from a fixed local datum, not from the riverbed. The datum may be above or below the actual riverbed, so gage height 5.2 ft doesn't mean the river is 5.2 feet deep — it means the water surface is 5.2 feet above the gauge's reference point. Gage height is primarily used to trigger flood warnings (when it exceeds the flood stage threshold).

How accurate is the data?

USGS stream gauge data is highly reliable — USGS is the gold standard for hydrological monitoring in the US. Most gauges are accurate to within 10% of true discharge under normal conditions. Accuracy may decrease during extreme floods (when the water is outside the range of the rating curve) or when gauges are damaged. USGS flags estimated and provisional data in their system.

Is this data real-time? Is there a delay?

Yes, data is near-real-time. USGS publishes new readings through the day from each gauge. StreamFlowData.com fetches this data from the USGS NWIS IV API hourly and caches it with a 1-hour TTL, so the reading you see is at most about an hour old. The "updated X ago" timestamp on each station page shows when the reading was last received.

Where does the data come from?

All streamflow data is sourced from the USGS National Water Information System (NWIS), a free public resource operated by the U.S. Geological Survey. StreamFlowData.com is not affiliated with USGS — we present publicly available data in a more readable format. See our Data Sources page for details.

See also: Streamflow Glossary • Articles • Data Sources