The Colorado Water Quality Control Commission is vested with the responsibility of developing regulations for the protection of aquatic life from, among other factors, the effects of metals due to historical mining activities. A tremendous number of factual considerations have led to varying water quality classifications and standards decisions. Furthermore, the Commission, a dynamic entity whose membership and staff are subject to change, must implement a continually evolving water quality policy. The following discussion is provided to furnish the Commission with a review of past policy decisions to aid in the continuity and consistency of their decision making. The principal focus of this assessment is on a sample of stream segments affected by metals as a result of historical mining activities. Particular attention has been paid to the determination of aquatic life use classifications and the resulting metals standards. Review of the Commission's archives indicates that decisions on water quality use classifications and metals standards for streams impacted by historical mining activity are established with varying levels of data and confidence in that data. Of the researched segments, this ranges from extreme confidence, as in the case of segment 3 a of the Alamosa River, to considerable optimism as demonstrated by the decisions for Mosquito Creek. Certainty in the Commission's decisions often comes from documented evidence, such as a use attainability analysis (UAA). Conversely, optimism frequently arises from major funding for remediation. Events external to the control of the Commission, primarily federal in origin, such as Superfund listing, can result in uncertainty in the level of future remediation attainable. The Commission may, therefore, be left with insufficient factual information to yield enduring decisions. The factual or policy factors that the Commission considers in making their decisions are varied and many. These include, but are not limited to, the present uses, the physical, chemical, and biological characteristics of a segment, federal and state statutes, clean-up plans and goals, water quality objectives, downstream classifications, wastewater management plans (208 plans), public comment, resource availability, the actions of other agencies, social impacts, and economics. From this broader list, the principal factors that appear to have been decisive in the Commission's standard setting for streams impacted by historical mining operations are: (1) the availability of information regarding the attainability of aquatic life uses and specific water quality levels, (2) the economic impact of more stringent standards, (3) the availability of external resources for remediation, (4) the actions of federal agencies including EPA oversight, (5) the degree of community involvement and support for remediation and (6) the ongoing refinement and evolution of their own policy.