Fixed site assessments are the primary source of information for assessing the water quality of streams in the Upper Mississippi River Basin study unit. Thirteen stream sites were sampled from 1996-1998 during the high intensity phase of the study. Three sites were sampled during the initial phase of low intensity sampling phase of the study from 1999-2004, and currently two sites are sampled. The sites are divided into three groups: integrator, indicator, and reference sites. Integrator sites were located on the Mississippi, Minnesota, and St. Croix Rivers and represented stream water-quality conditions in heterogeneous, large basins that are affected by combinations of land-uses, point sources, and natural influences. Integrator sites also included major locations in the drainage system for large-scale transport analysis. Indicator sites were located on smaller streams that represent stream water-quality conditions in basins with fairly homogeneous land use and physiographic conditions. Most indicator sites were further grouped by the underlying surficial geology: glacial outwash or glacial till. Reference sites were located downstream of undisturbed areas that represent selected ecoregions or environmental settings within the study unit.