This paper describes the development of a guidance tool for assessing the ability of a receiving watercourse to assimilate pollution from point discharges. The ‘sustainable capacity tool’uses a framework that accounts for the ‘no‐deterioration’requirement of the Water Framework. Directive, in terms of the downgrading of a river‐stretch classification and the requirement to return all rivers to ‘good ecological status’. The second requirement results in a long‐term set of river‐quality targets or objectives, and it is generally assumed that ‘good’refers to ‘A2 quality in the Scottish Environmental Protection Agency classification system. The resulting sustainable capacity is defined as the risk‐based amount of capacity that could be allocated without causing a failure of the target class and which could also result in a negative capacity if the river stretch is currently failing the target class. This is plotted as a GIS layer and is intended to form an overview of water quality to help inform stakeholders who are participating in a water‐quality strategy for the next Scottish investment programme on Quality and Standards 3. The sustainable capacity tool could be used in conjunction with integrated catchment modelling for complete management of the Water Framework Directive river‐basin districts.