Description: The Oregon Stream Classification provides a stream/watershed classification system for streams and rivers in Oregon. Stream classes reflect both the local (assessment unit) and watershed (integrative) scale, and reflect broad functional expectations based on basic hydrologic and physical characteristics and determinants of flow regime. To provide a limited number of classes for easier comparison for some applications, an exclusionary rule set for 17 (local assessment unit) types using classification parameter values that the local units share in common was developed. These types describe 17 subsets of local unit groupings that have similar landscape position, water budget, and seasonal hydrology.