We tested the effects of transport containers and transport water treatments on the survival of field-collected delta smeltHypomesus transpacificus, a threatened osmerid endemic to the Sacramento–San Joaquin estuary in California. Use of cylindrical polyethylene bags instead of rectangular coolers as transport containers increased survival from 40.7 to 83.6% at 4 h postcollection, from 11.9 to 33.1 % at 48 h, and from 6.9 to 27.9% at 72 h. Addition of NovAqua, a commercial water conditioner containing polymers, to transport water of 8‰ NaCl significantly increased 72-h survival (54.8%) over that of the 8‰ NaCl control (27.9%). Survival of fish lightly anesthetized with MS-222 (tricaine methanesulfonate) during transport was intermediate between the NaCl and NaCl plus NovAqua treatments. Survival of delta smelt in the NaCl plus NovAqua treatment also improved from August through November, as fish increased in size and water temperature decreased. Improved survival of delta smelt treated with NovAqua was probably related to the polymers, which may have reduced physiological stress responses, such as osmotic imbalance.