As a first step towards the restoration of the Ranchería River (La Guajira-Colombia), we have set Water Quality Objectives (WQO) with a systematic methodology. This methodology consists of initially establishing desirable WQO, consistent with current and potential uses; then it is checked whether the current quality status meets them; afterwards, a feasible sanitation plan is defined for the medium-term (acting on point-wise loads) and for the long-term (on diffuse loads) trying to attain the chosen OCA. Through water quality simulation model (QUAL2KW in our case), suitably calibrated, the corresponding level of achievement of such desirable OCA is hence assessed. Typically, it is necessary to reduce the expectations (WQO targets), especially in the long-term because they can only be achieved with challenging interventions on diffuse sources. The newly determined targets are hence the operational ones. However, also the desirable OCA are useful as a stimulus for start a long-term process. The proposed methodology is useful for any Water Resource Management Plans (WRMP) in Colombia and also in other countries as it avoids the usual error of setting non-attainable WQO that leads to frustration and sometimes to escaping to comply with environmental responsibilities.