This paper illustrates the importance of valuing environmental goods and services associated with water quality improvements when assessing implementation of on-farm nutrient management plans as required by the Quebec Regulation Respecting Agricultural Operations (RRAO). Based on a case study in the Chaudiere River watershed, two scenarios were considered using the integrated, economichydrological, modelling framework provided by GIBSI: (i) a base-case scenario assuming application of all available manure; and (ii) an on-farm nutrient management scenario based on meeting phosphorus crop requirements with manure and treating any manure surpluses. Two types of management units were selected to evaluate these scenarios: (i) contiguous municipalities (administrative units of agricultural development); and (ii) subwatersheds. Results showed that management at subwatershed levels had larger benefit/cost (B/C) ratios when compared to contiguous municipalities. This illustrates that the watershed is a more meaningful management unit than the municipality, which is not a hydrological unit. For one of those subwatersheds, the B/C ratio was close to one although only various recreational benefits were accounted for in the evaluation. In all likelihood, if a more holistic set of benefits were accounted for, a B/C ratio greater than or equal to one would have resulted. A sensitivity analysis revealed that variations of 37.5%, -22.5%, and -20% for monetary benefits, on-farm manure treatment costs, and average probabilities of exceeding the targeted water quality standard (prevention of eutrophication of rivers), respectively, were necessary to obtain a B/C ratio greater than one.