Two in-situ exposure studies were conducted with the federally-listed endangered Rio Grande silvery minnow (Hybognathus amarus). One-year-old adults were exposed in cages deployed at three sites in the Middle Rio Grande, N. Mex., for 4 days to assess survival and for 26 days to evaluate survival, growth, overall health, and whole-body elemental composition. The test sites were located on the Pueblo of Isleta in the (1) main channel of the Middle Rio Grande, (2) 240-Wasteway irrigation return drain, and (3) wetted instream habitat created below the outfall of the 240-Wasteway irriga-tion return drain.