I frequently kayak the Potomac River and the real-time stage data reported by USGS seem to be too high (or too low). Are the USGS data inaccurate?
There may be occasional equipment or database problems where erroneous data are reported for short periods of time until corrections can be made. This is why it is important to look at a record of streamflow such as the 7-day hydrograph plots rather than a single point in time. However, most of the time USGS has a high level of confidence in its real-time stage data.
During low streamflow conditions, aquatic grasses may produce increases in stream water level near gages. On smaller streams, debris or rocks on flow control structures may also produce increases in water level. Stage values reported on these pages are believed to be reasonably accurate, but the higher stage readings may produce estimates of discharge that are higher than actual. These higher stage readings at stream gages may be localized and may not be good indicators of stream stage at other locations on the river.
During extreme cold weather, ice can affect stage and discharge determinations at some stream-gaging stations. Data values reported by USGS may be significantly higher or lower than actual streamflow. Adjustment of data for ice effects can only be done after detailed analysis.