Detroit Lake is a large reservoir on the North Santiam River in west-central Oregon. Water temperature and suspended sediment are issues of concern in the river downstream of the reservoir. A CE-QUAL-W2 model was constructed to simulate hydrodynamics, water temperature, total dissolved solids, and suspended sediment in Detroit Lake. The model was calibrated for calendar years 2002 and 2003, and for a period of storm runoff from December 1, 2005, to February 1, 2006. Input data included lake bathymetry, meteorology, reservoir outflows, and tributary inflows, water temperatures, total dissolved solids, and suspended sediment concentrations. Two suspended sediment size groups were modeled: one for suspended sand and silt with particle diameters larger than 2 micrometers, and another for suspended clay with particle diameters less than or equal to 2 micrometers. The model was calibrated using lake stage data, lake profile data, and data from a continuous water-quality monitor on the North Santiam River near Niagara, about 6 kilometers downstream of Detroit Dam. The calibrated model was used to estimate sediment deposition in the reservoir, examine the sources of suspended sediment exiting the reservoir, and examine the effect of the reservoir on downstream water temperatures.