A software patch was posted on June 29, 2016, which should have remedied the bug described below. Testing after installation of the patch has not found any new incidences of the problem. However, as the problem was intermittent, it is still possible new incidences could be found. Users should submit a support request to the StreamStats team from the Help link on the user interface if additional instances of this problem are found. 

From June 15, 2016:

A user found on June 15, 2016, that StreamStats for Illinois is occasionally giving incorrect results for some basin characteristics and flow statistics.  The StreamStats development team is working to determine why this is happening and correct it. Occasionally, StreamStats is not computing stream slope and basin length correctly, and subsequently, as those basin characteristics are used as explanatory variables in the regression equations for estimating peak-flow statistics, the estimates also are incorrect. Until this warning is removed, users should always compute all basin characteristics when also obtaining flow estimates. If the basin characteristics output table indicates that the value of BASLENRAW (raw basin length) is zero, then disregard the results for that site.