This report will assist states and authorized tribes--and the associated communities--to understand how the assessment of ecological benefits can help to support their water quality decisions while complying with the provisions of the Clean Water Act (CWA). The report is intended to assist water quality officials, watershed managers, members of stakeholder groups, and other interested individuals in fully evaluating ecological and socioeconomic objectives and the gains and losses that often are involved. Under the CWA, states and tribes adopt water quality standards (WQS). This includes setting designated uses or goals for their water bodies. When natural, man-made, or socioeconomic factors preclude the attainment of a designated use, the CWA recognizes that states and tribes must do an evaluation before changes to a designated use can be made. In certain cases, depending on the factor, the evaluation focuses on the costs and impacts (i.e., losses) of achieving the designated use. However, decisions related to changing or attaining designated uses sometimes involve both gains and losses (or benefits and costs) among health, ecological, institutional, and socioeconomic considerations.