The NHD-Plus project was initiated by EPA and USGS to facilitate consistent national and interstate stream assessments. The NHD-Plus hydrography layer provides a unique spatial code for each stream reach within the U.S. and is used for a rapidly growing number of applications. Some advanced user groups have developed databases comprised of reach-scale descriptors (e.g., elevation, slope, drainage area, etc.). Hundreds of those descriptors now exist and can be used with the NHD-Plus and NSI networks as predictor variables in stream analyses. Brief descriptions of those databases and hyperlinks to relevant websites or contact persons knowledgeable about accessing the data are given.