This report contains initial results from the Diagnostics Committee, produced under the U.S. Environmental Protection Agency (EPA) Aquatic Stressors Framework (USEPA, 2002a). The Diagnostics Workgroup has developed conceptual models for four major aquatic stressors that cause impairment: nutrients, suspended and bedded sediments, toxics, and altered habitat. The conceptual models form the basis for classification of aquatic systems according to their sensitivity to these stressors. The proposed classification framework should enable a more refined approach for quantifying stressor-response relationships over broad geographical scales. A coastal classification framework was constructed which encompasses watersheds and coastal wetlands in both Great Lakes and marine coastal states in the conterminous U.S. This report provides an overview of the components of the classification framework: (1) a review of existing classification schemes and examination of their relevance for different management goals, (2) a conceptual model for classification based on risk from stressors, (3) coastal classification databases for both Great Lakes and marine coastal states, (4) a description of potential approaches to classification, (5) application of an empirical approach for classification to coastal estuarine systems, (6) a regional test of a watershed classification framework based on data from Lake Michigan coastal riverine wetlands, and (7) plans for Stage II of the coastal classification framework.