The Bonneville Power Administration developed this SEIS to evaluate potential impacts resulting from construction of a 4,700-foot segment of the Ashe-Slatt transmission line at Crow Butte Slough, overhead on towers on the existing right-of-way. This SEIS is a supplement to DOE/EIS-0077, Ashe-Slatt (Pebble Springs) 500-kilovolt Transmission Line, originally filed as FES 75-79.