On a local scale, the biota of the Plummers Island, Maryland, vicinity is among the most intensively studied in the world. The fishes occurring in Potomac River and its tributaries in the vicinity of that island have been subjected to periodic scrutiny since the early 1900s, with the latest thorough analysis published in 2002. Herein, we present an updated and comparative analysis of this fish fauna using data gathered over the past decade. Our findings reveal that the complement of fish species that inhabits the area is particularly dynamic in nature. Compared to data presented in 2002, we report a net increase in the numbers of species (up to 93 species) occurring or formerly occurring near Plummers Island. These changes are the result of the return of several migratory species fostered by improved fish passage on the Potomac River, the return of some native resident fishes, and the establishment of additional nonnative species that now constitute 22–35% of the fauna, balanced against several probable extirpations. Species involved in these changes are treated in detail, and a number of novel records, vouchered and nonvouchered, are discussed. Factors that likely play key and interrelated roles in the dynamic nature of the Plummers Island area fish fauna, including hydrographic context and anthropogenic activities, are revisited and discussed. Particular emphasis is placed on the importance of improved practices in the documentation of local species occurrences in the future.