The Texas Water Resources Institute (TWRI), Texas AgriLife Research, the Texas AgriLife Extension Service, and Texas A&M University-Kingsville conducted an Arroyo Colorado nonpoint source assessment of agricultural sources. Since the Arroyo Colorado Watershed Protection Plan has been completed, the Arroyo Colorado Watershed Partnership has worked to implement best management practices on cropland to reduce the amount of nutrients entering the Arroyo Colorado. This program focused primarily on evaluating the effectiveness of best management practices on row crop fields, evaluating nutrient removal in vegetated drainage ditches, and determining which management practice scenarios would be most effective in keeping nutrients from entering the Arroyo. The program team found that two management practices, nutrient management and irrigation management, were the most effective practices in keeping nutrients from running off cropland and into drainage ditches. Drainage ditches were monitored, and it was determined that they could act as constructed wetlands by removing nutrients through natural processes if properly maintained. If not properly maintained, drainage ditches could release nutrients, previously absorbed, back into the water that eventually makes its way into the Arroyo. Scenarios were modeled using the Soil and Water Assessment Tool (SWAT) that demonstrated which suite of practices through 2025 need to be adopted to provide necessary loading reductions. Lastly, the land use data for the Arroyo Colorado Watershed was updated and used as an input file to the SWAT model and can be used in a variety of other methods.