The South Platte River (CO) was an effluent-impacted river that was effluent-dominated at times of the year (when background river flow was low). EfOM from the WWTPs that discharged into the river was a source of DOC and DON, as well as DBPs and their precursors. However, the reactivity of the EfOM to form many halogenated DBPs (THMs, HAAs) was less per unit of DOC than that of the river water. That is because the EfOM had a lower percentage of the bulk DOC as humic substances. On the other hand, the EfOM was richer in DON and precursors for nitrogenous DBPs (e.g., HANs, nitrosamines). At the Littleton/Englewood WWTP and the Denver Metro WWTP/North Complex, treatment processes with nitrification not only lowered the ammonia content of the wastewater, but also reduced the levels of DON and precursors for the HANs and the haloacetaldehydes. Because the City of Thornton (CO) took their water from a canal upstream of the Denver Metro WWTP, the impact of treated wastewater on their drinking water supply should not have been as great as compared to the site downstream of the latter WWTP. In this project, DBP and nitrosamine FP tests, along with the DON method and miscellaneous advanced NOM characeterization techniques, were used (in part) to characterize DBP precursors in treated wastewater. In addition, primidone was found to be a good indicator of wastewater contributions to the river flow. These tools can be used by the wastewater and drinking water industry to better understand the impact of treated wastewater on DBP precursor loadings in a local watershed.