I use 2 sources for river flow data. the first is the Federal USGA.
Its coverage is backed by a long archive, but little fine grain
coverage of smaller rivers and tribs. The Feds also do a neat
forecast.

http://waterdata.usgs.gov/wa/nwis/current/?type=flow

My second source is the Washington State Dept of Ecology flow
monitoring network.

https://fortress.wa.gov/ecy/wrx/wrx/...ions/state.asp

The best stuff comes from the automated 112 systems that use telemetry
to post 15 minute apart readings of CFS, water and air temps, to the
State DOE web site.

Flood warning seems to be a significant factor in allocation, and
deployment pattern of the stations.

Whats the arrangement, availability etc of river flow data in other
states? On line? graphic? etc.