Impoundments, diversion dams, and stream dewatering have created a mosaic of largeriver fragments throughout the Great Plains of central North America. Coincident with thesehabitat changes are massive declines in the distribution and abundance of Great Plains fishesbelonging to the 'pelagic-spawning' reproductive guild. We analyzed longitudinal fragmentlengths (measured in river kilometers, rkm) and literature accounts of population status for eightspecies from this guild across 60 fragments to derive thresholds in stream length associated withextirpations. Fragment length predicted population status (F2,21 = 30.14, P < 0.01), with lengthsaveraging 136 ± 21 rkm for extirpated, 226 ± 69 rkm for declining, and 458 ± 137 for stablepopulations. Fragment length explained 71% of reported extirpations and estimated thresholds infragment length explained 67% of variation in population persistence. Our findings provide insightinto appropriate spatial scales for conducting riverscape conservation approaches that addressthe hierarchical effects of fragmentation on stream-dwelling fishes.