Citizen science as a long-term environmental baseline: assessing impacts of a small dam removal in Montana, USA

Abstract. As dam removals increase in frequency across the U.S., most research has focused on the impact of larger dam removals, despite the removal of small dams being much more common. There are hundreds of small dams in Montana, and this research investigates impact on stream ecology and morphology using citizen science data collected over eight years spanning before and after a 2020 small dam removal in Rattlesnake Creek. We analyzed pebble count grain size distributions and aquatic macroinvertebrate biotic indices from 2017 to 2024 to assess changes in sediment transport and macroinvertebrate population as well as evaluate the efficacy of citizen science for long-term stream monitoring. Our analysis includes comparisons of pre– and post–dam removal data collected from above and below the dam site. Our findings revealed no significant changes in grain size or macroinvertebrate index values between upstream and downstream reaches post–dam removal, suggesting that the removal of this small dam had minimal detectable impact on sediment transport and macroinvertebrate communities within the study period. Our study also demonstrates the capacity for citizen science programs to effectively collect robust and valuable datasets. This study underscores the importance of meticulous data management along with the potential for, and challenges of, citizen science for environmental research. We provide recommendations for "best practices" to improve future citizen science monitoring and informing decision-making for future dam removals, particularly for the nine dams further upstream within the Rattlesnake Creek watershed.