Arctic grayling (Thymallus arcticus) have a life-history strategy specifically adapted to the extreme climate of the North. These fish migrate to spawning grounds just after breakup in the spring, then migrate to feeding sites in early summer, and finally in the fall migrate back to their overwintering sites. The Kuparuk River is a perennial stream originating in the northern foothills of the Brooks Range on the North Slope of Alaska. Sections of the Kuparuk are periodically intermittent in that, during low flows in the system, these channel reaches appear dry. The flow varies between surface and subsurface in this permafrost-dominated environment, with subsurface flow being limited to the unfrozen thaw bulb around the stream. These dry reaches create a barrier to fish migration due to the lack of surface channel flow. The impacts of a warming Arctic may have implications for the partitioning of flow within the Kuparuk and consequently affect the ability of fish to move within the system at critical times. The timing and duration of these barriers are sporadic, occurring with almost equal probability throughout the summer, with fall dry spells creating the biggest impact on Arctic grayling fitness.