About StreamFlowData.com

StreamFlowData.com answers a simple but surprisingly hard question: is this river high or low right now?

A raw discharge number — 12,500 CFS at Lee Ferry on the Colorado River — is meaningless without context. Is that high for April? Low for this year? Dangerous? Great for fishing? StreamFlowData.com provides that context automatically by computing the percentile rank for every reading against decades of historical data for the same calendar date.

The Data

All data comes from the USGS National Water Information System (NWIS), a free public resource maintained by the U.S. Geological Survey. USGS operates over 8,000 stream gauges nationwide, transmitting readings throughout the day via satellite.

We present three layers of data:

• Real-time readings — instantaneous discharge (CFS) and gage height (ft), refreshed hourly from the USGS IV service
• Historical daily values — mean daily discharge for the past 90+ days, sourced from the USGS DV service
• Long-term statistics — percentile thresholds (10th, 25th, 50th, 75th, 95th) for each calendar day, based on the full period of record at each gauge

Who Uses This?

StreamFlowData.com is built for anyone who cares about rivers:

• Anglers checking whether flows are fishable before making the drive
• Kayakers and rafters who need to know if the river is too low, perfect, or dangerously high
• Emergency managers monitoring flood conditions across a state or watershed
• Hikers and campers planning trips near rivers or needing to ford crossings
• Hydrologists and scientists wanting quick access to current conditions
• Curious people wondering why the creek behind their house is running brown and high

How Percentile Rank Works

For each station and calendar date, USGS has decades of historical daily mean discharge values. We compare today's reading to those historical values to determine what fraction of historical years had lower flow on this date. A percentile of 50 means perfectly normal — half of all historical years on this date had lower flow. A percentile of 5 means an extreme low — only 5% of years were lower.

We use five categories:

Disclaimer

StreamFlowData.com is an independent project and is not affiliated with the U.S. Geological Survey (USGS), NOAA, or any government agency. While we strive to present data accurately, do not rely solely on this site for flood safety decisions or water entry. Always check official USGS and NWS resources and exercise independent judgment before entering any body of water.