This paper briefly describes the environmental component of an integrated modeling system that has been developed for simulating the movement of nutrients (nitrogen and phosphorus) from dairy waste disposal fields through the Upper North Bosque River Watershed (UNBRW) stream network in Erath and Hamilton Countries, Texas, as part of the "Livestock and the Environment: A National Pilot Project" (NPP). The environmental component consists of the Agricultural Policy/Environmental eXtender (APEX) model and the Soil Water Assessment Tool (SWAT). The APEX model is designed to simulate the edge-of-field nutrient runoff and leaching loadings from the application of solid and liquid manure on dairy waste disposal fields that are subsequently routed through the UNBRW stream system in SWAT to the watershed outlet near Hico, Texas. The basis for selecting APEX and SWAT, and the linkages between the two models, are emphasized within the context of the UNBRW modeling system configuration. A brief overview of the watershed characteristics and the in-stream water quality monitoring system installed on the UNBRW stream network is also presented. This monitoring system provides a key data set that has been used to calibrate the environmental modeling component for current conditions in the watershed.