Low streamflows and warm stream temperatures, caused mainly from agricultural diversions, currently limit available habitat and productivity of trout, including native Lahontan cutthroat trout in Nevada’s Walker River Basin. Environmental water purchases, which transfer water from willing sellers to instream uses (i.e for fish), are being evaluated to improve instream habitat. To determine which environmental water purchases to prioritize, this study was undertaken to build a computer model in order to simulate stream temperatures under differing environmental water transfer scenarios. Model runs simulate a range of environmental water transfers at major diversions and reservoirs throughout the Walker River Basin. Results indicate that low flows generally coincide with critically warm stream temperatures, cooler stream temperatures exist in the East Walker River, a tributary of the Walker River, during warm seasons which provide good habitat for fish, environmental transfers can improve stream temperatures for some highly impacted reaches by up to 3°C in dry years, and environmental water transfers have a greater effect in dry years than wet years.