We quantified body morphology in individuals from 49 collections of spotfin shiner (Cyprinella spiloptera) in the Wabash River watershed. Ten morphological measurements were used to produce principal component (PC) axes that were examined for relationships with watershed area. Analyses of males and females resulted in sexual dimorphism for one PC axis that represented caudal fin length and head depth; both have increased size in males. An analysis of body shape with watershed area resulted in different relationships for males and females. Caudal peduncle length increased with stream size for males and decreased with stream size for females. No significant relationships were found for sexual size dimorphism (SSD) with stream size. Allometry for SSD supported Rensch's rule -male body size increased more rapidly than female body size with increased SSD. Morphology in spotfin shiners is constrained by a combination of sexual selection and the hydrologic regime of the watershed.