Appendix 5. Comparison of predicted and observed mean monthly water temperatures in the Lees Ferry (reach number = 1), Furnace Flats (6), and Lower Canyon (11) reaches. Lake Powell was impounded in March 1963 and completely filled in 1982. Discrepancy between observed and predicted values during the first 10 years of reservoir filling was caused by higher GCD outflow temperatures that were not modeled in our simulation.