The USGS has a system of gages that allow you to see the flow rates of water bodies, rivers, creeks, lake levels,.
With Google Earth you are able to zoom right into to a location once you know the coordinates. Combining these two tools, we can see right where a USGS gage is located and see if it will provide information to help you plan a trip. The gages will possibly be run in cooperation with one of more agencies to fund it. Those named agencies may have a hand in flows on the water in question so they too are a point of contact for additional information.
http://waterwatch.usgs.gov/index.php?id=real&sid=w__kml
However, you can use the link above to add to your Google Earth data base and see where USGS gages are located. These may not be the ONLY gages serving an area, but for me, they are the first place to look.
