Here are some alternatives to StreamStats, in case we have not yet implemented your area of interest:
If you want to get only a basin delineation, then you can use ESRI’s Watershed Explorer tool, which can be found at http://www.arcgis.com/home/item.html?id=bbd10d91da4f4ffbbdfd8db1d677053c. Use of this tool requires an ArcGIS Online account. Alternately, if you have a basin that is less than about 1.5 square miles, then you can use the USGS National Map Viewer to hand delineate the boundary and get the area. To do that, go to http://viewer.nationalmap.gov/viewer/, zoom into your location of interest, click on the Advanced tab above the map and then on the Area button, and then begin your delineation. Double-click to end it. The resulting area will be shown.
If you want a watershed polygon, that is quite a bit more complicated. There is a web service from EPA here:
You need to be a web developer, though, to figure out how to use that.
If you need to get the polygon, and you have access to ArcGIS 9.3.1. You can try the NHDPlus Basin Delineator Tool. You can get it here:
There is newer data (NHDPlus Version 2), and of course newer ArcGIS software (10.1), but the tools haven't been updated to work on either of those yet.