This database compiles data on environmental impacts mitigation costs for 182 hydropower projects based on documents obtained from the U.S. Federal Energy Regulatory Commission (FERC). Data for all measures (which are generally found in the “Developmental Analysis” section of the EA documents) as well as their associated economic information, FERC categorization, and final FERC decision were collected. Due to differences in file type (i.e. PDF, Microsoft Word document, or image) and structure (i.e. different table formats, page and section numbering styles, and section titles), each EA document was manually investigated and all relevant PM&E data were consolidated in a Microsoft Excel Workbook, referred to below as the EA Cost Database.