Lack of integration of geomorphologic, hydraulic, and ecological criteria has hampered efforts to implement holistic approaches to stream restoration. We propose a design framework called stream naturalization that integrates geomorphology, hydraulics and ecology to improve the environmental quality of degraded streams. Research to support naturalization has focused on agricultural streams in East Central Illinois. This paper compares physical and biological conditions in meandering and straight reaches of a 3rd order stream. The meandering reach exhibits greater three-dimensional habitat structure compared to the straight reach. Fish density, biomass, and diversity also are greater in the meandering reach compared to the straight reach. Together these findings suggest that stream geomorphology, through its influence on habitat diversity, has an important influence on fish community structure. Naturalization designs that incorporate varied, but stable, geomorphological conditions, should, by enhancing habitat diversity, increase fish biomass and species richness. Copyright ASCE 2004.