BIO-WEST has been evaluating the size, distribution, and permanence of native fish populations both below and (most recently) above the Wells-Siding Diversion on the lower Muddy River in Nevada. During previous monitoring efforts, fish populations were found to be predominantly composed of nonnative species, but in 2003, 18 Virgin River chub (Gila seminuda) were found immediately below the diversion, which stimulated a comprehensive sampling effort. BIO-WEST used seines, hoop nets, minnow traps, and backpack electrofishing for these efforts. BIO-WEST also evaluated stream discharge and temperature as indicators of habitat suitability for the permanence of native fish populations in this reach. Most recently this effort was expanded to the upper portions of the Muddy River, which constitutes the most complete and holistic sampling of this system since historical collections were made in the 1960s and 1970s.