Wunderground Wundermap showing river gages

LINKJust check the box next to USGS river to the right of the page/
Pretty handy little tool.
Here's an example of the info accessible

Station ID: 07374000
Name: Mississippi River at Baton Rouge, LA
Flow Rate: 1314000.00 cfs
Percentile: 96%
Temperature: 32.00 F
Stage: 43.33 ft
Forecast Stage: 44.5 ft
Flood Stage: 35 ft