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Nutria are large, semi-aquatic rodents first introduced into the United States from South America as a fur resource during the 1890s. Nutria first were reported at Rio Grande Village, Big Bend National Park, in 1993. During 2004 and 2005, more than 30 locations of nutria activity were documented along a 16 km section of the Rio Grande River from 7.6 km upstream of Rio Grande Village to Boquillas Canyon including the Rio Grande Village beaver pond. Seventeen nutria were captured, marked, and released. Using the Schnabel and Chapman methods, 38-74 nutria were estimated to inhabit the RGV area. Stomach contents (n = 14) contained common reed (Phragmites australis), water pennywort (Hydroctyle umbellata), giant reed (Arundo donax), spikerush (Eleocharis caribaea), bermudagrass (Cynodon dactylon), water hyssop (Bacopa monnieri), foxtail (Alopecurus sp.), and flatsedge (Cyperus sp.). Seven adult nutria were radio-collared and released between May 2004 and June 2005. The mean home-range size was estimated to be 10.0 ha (14.8 ha for males, 2.9 for females), and the mean maximum daily distance moved was estimated to 637.4 m (738.3 m for males, 486 m for females).