Dam It, I’m Stranded: Evaluating Fish Stranding Downstream of Two Hydropeaking Dams in Northern Ontario

ABSTRACT Globally, there has been an increase in the development and use of hydropower to produce energy. Hydropeaking is an operating regime that is used to meet real‐time energy demands; however, daily fluctuations in flows may result in fish becoming stranded. Understanding physical and operational factors that contribute to fish stranding will aid in the creation of mitigation strategies to prevent fish stranding occurrences. Here we investigated factors that drive fish stranding. To do so, we deployed cameras downstream of two hydropeaking generating stations in northern Ontario, Canada, from June to October in 2023 and 2024, to remotely capture occurrences of fish stranding. We observed significantly higher fish stranding densities (fish m −2 ) on the Michipicoten River compared to the Magpie River. Stranded fish were difficult to identify to species (from the camera images) but in general, fish were small‐bodied, likely representing early life stages (e.g., juveniles). The probability of fish stranding was highest in the early spring and increased with both finer substrate types and slower horizontal ramping rates (cm h −1 ). The observed differences in fish stranding densities between the two rivers are likely due to physical features such as the absence of morphological microstructures, larger substrate types, and the presence of a plunge pool (at one site). The plunge pool likely dampened the change in discharge from the dam, which subsequently decreased the vertical ramping rate (cm h −1 ) downstream. The model we generated will allow for comparison with other hydropeaking systems globally to better understand if factors driving fish stranding are common among rivers to help identify potential mitigation strategies to minimize stranding.