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USGS - science for a changing world

Streamgage Information

The U.S. Geological Survey has been measuring streamflow in the U.S. for over 120 years. We operate more than 7,500 streamgages in the U.S. and nearly 500 in California.



Learn about ways that streamgages help citizens every day.


Automated Local Evaluation in Real-Time (ALERT) Gages

Many of the USGS streamgages in California are Automated Local Evaluation in Real-Time (ALERT) gages. ALERT gages are designed to send an automated warning when water levels reaches predetermined levels or change rapidly.

These water levels can signify potentially hazardous conditions for downstream locations. ALERT data are streamed in real-time to the National Water Information System (NWIS-web), and are used by the National Weather Service for model forecasting and to issue flood warnings.

The USGS California Water Science Center recently added several ALERT gages and precipitation stations in the burn areas of the Valley and Butte Wildfires to help monitor the potential for mudslides and debris flows, and to provide early flood warning to downstream areas.

California Streamgage Network