Abstract We assessed the influence of land cover at multiple spatial extents on fish assem- blage integrity, and the degree to which riparian forests can mitigate the negative effects of catchment urbanization on stream fish assem- blages. Riparian cover (urban, forest, and agri- culture) was determined within 30 m buffers at longitudinal distances of 200 m, 1 km, and the entire network upstream of 59 non-nested fish sampling locations. Catchment and riparian land cover within the upstream network were highly correlated, so we were unable to distinguish between those variables. Most fish assemblage variables were related to % forest and % urban land cover, with the strongest relations at the largest spatial extent of land cover (catchment), followed by riparian land cover in the 1-km and 200-m reach, respectively. For fish variables re- lated to urban land cover in the catchment, we asked whether the influence of riparian land cover on fish assemblages was dependent on the amount of urban development in the catchment. Several fish assemblage metrics (endemic rich- ness, endemic:cosmopolitan abundance, insec- tivorous cyprinid richness and abundance, and fluvial specialist richness) were all best predicted by single variable models with % urban land cover. However, endemic:cosmopolitan richness, cosmopolitan abundance, and lentic tolerant abundance were related to % forest cover in the 1-km stream reach, but only in streams that had < 15% catchment urban land cover. In these cases, catchment urbanization overwhelmed the potential mitigating effects of riparian forests on stream fishes. Together, these results suggest that catchment land cover is an important driver of fish assemblages in urbanizing catchments, and riparian forests are important but not sufficient for protecting stream ecosystems from the im- pacts of high levels of urbanization. Keywords Riparian buffer Æ Catchment Æ Urban Æ Land use/cover Æ Land–water interface Æ Piedmont Æ Stream Æ Fish A. H. Roy Institute of Ecology, University of Georgia, Athens, GA 30602, USA B. J. Freeman Georgia Museum of Natural History and Institute of Ecology, University of Georgia, Athens, GA 30602, USA M. C. Freeman US Geological Survey, Patuxent Wildlife Research Center, University of Georgia, Athens, GA 30602, USA Present Address: A. H. Roy (&) U.S. Environmental Protection Agency, 26 West Martin Luther King Drive, MS 498, Cincinnati, OH 45268, USA e-mail: roy.allison@epa.gov Landscape Ecol (2007) 22:385–402 DOI 10.1007/s10980-006-9034-x 123 RESEARCH ARTICLE Riparian influences on stream fish assemblage structure in urbanizing streams Allison H. Roy Æ Byron J. Freeman Æ Mary C. Freeman Received: 15 April 2005 / Accepted: 17 August 2006 / Published online: 21 November 2006 Ó Springer Science+Business Media B.V. 2006