Marshallia pulchra is a globally rare forb endemic to riverscour ecosystems within high-gradient rivers in the Appalachian Plateau of eastern North America. Given the high conservation priority and limited ecological understanding of M. pulchra, we sought to establish knowledge pertaining to the hydrologic conditions of sites supporting this species. We assessed flow records for 10 rivers to determine if climate change is modifying flood frequency, magnitude, or duration of M. pulchra–supporting rivers. Records in the Youghiogheny River were also linked to cameras trained on individual plants to quantify the flood frequency and duration sustained annually. Finally, we used a century of M. pulchra presence/absence data from the Youghiogheny River to assess long-term persistence. Discharge records indicate that floods in smaller, free-flowing rivers are becoming more frequent at a rate of up to one flood per year. However, we detected no trends suggesting that floods are becoming more intense. M. pulchra individuals in the Youghiogheny are inundated a median of 17 times annually, mostly during winter and spring, and usually for periods less than 2 d. Results suggest that the long-term viability of M. pulchra in the Youghiogheny may be diminishing, as individuals were absent in nearly 40% of previously occupied sites during the most recent surveys. Given the signs of population decline in the Youghiogheny, additional investigations exploring the hydroecology of M. pulchra are urgently needed, especially those that consider the role of invasive species in changes to riverscour ecosystem dynamics.