External nutrient loading is a key driver of phytoplankton growth in freshwater ecosystems and loading data across varying ecosystems is sparse. However, new tools are emerging that can provide accurate estimates of nutrient loading based on readily available landcover, point source discharge and long-term rainfall patterns. Here we utilized the publicly available geospatial watershed modeling platform: Model My Watershed (MMW), to acquire watershed scale loading rate estimates for major Texas freshwater reservoirs. We compared these modeled estimates to measured estimates from a small number of Texas lakes and reservoirs and to the broader range of estimates for lakes and reservoirs globally from scientific literature. We also related the modeled loading estimates to data from the Texas Commission on Environmental Quality’s (TCEQ) Trophic State Index (TSI) database to examine relationships between phosphorus inputs and lake tropic status. The results of this research aim to advance our understanding of the variation in nutrient loading across the large Texas climate gradient and identify nutrient load reduction goals based on adopted water quality screening levels for trophic state (as chlorophyll-a) in the state of Texas.