Ideal observation sites are located near tributary-mainstem confluences and provide frequent,synchronous measurements of physical, chemical, and biological attributes. This “nested watershed”design supports characterization of environmental conditions adjacent to the sampling stations, whileinstream hydrological measurements will reflect both local conditions and inputs from upstream. TEON observations sites are stratified by ecoregions, so we can aggregate data sets across the network to characterize conditions at the ecoregion scale.