USGS gauge
A streamflow measurement station operated by the United States Geological Survey. Each gauge publishes real-time flow rate (CFS), gauge height (feet), and sometimes water temperature, available freely via the USGS Water Services API.
USGS gauges are the canonical source for river-flow data in the U.S. The Great Lakes steelhead fishery has approximately 53 USGS gauges across 31 actively-fished tributaries — some rivers have multiple gauges (the Cuyahoga has 9). Gauge data updates every 15 minutes. Steelhead Addiction pulls every gauge for every covered river and adds the interpretation layer (percentile ranks, optimal zones, fishability ratings).
