The objective of this study was to add to a traditional forest planning model by incorporating some consideration of the effects of forestry on dissolved organic carbon (DOC) concentrations in streams over time. In a case study, for a watershed in northern Sweden, we present the best possible solution to a forest planning problem that maximizes the net present value (NPV) while the DOC concentration levels in the watershed are maintained below a defined threshold value. Results from the case study show that the decrease in NPV, when taking DOC into account, was considerable. However, the decrease in possible harvest volume was restricted in the case study area because the model moved harvesting activity from the first 20-year period to later periods to avoid high initial DOC concentrations. The model presented could be a useful tool for predicting the effect of forestry on DOC concentrations over time.