Weirs or run-of-river dams can disrupt bedload transfer with negative ecological effects downstream due to sediment starvation. The way and the degree to which bedload is trapped is nevertheless not straightforward and few studies have examined this topic. This study focuses on a 13-km-long reservoir of the Rhône River, France, created by a diversion dam equipped with bottom gates. Our main objective was to determine the degree of alteration of the bedload transfer downstream and to identify to which extent the implementation of Ecomorphogenic Flow (EmF), defined as environmental flow whose objective is specifically to increase bedload transfer through the reservoir to promote downstream habitat diversity, could increase bed mobility. The results show that the potential for morphological adjustments in the reservoir was already low before dam completion (1968) in response to a substantial decrease in coarse sediment supply, but that this potential was progressively reduced due to the impoundment. However, the bedload transfer continuity has been at least partially maintained since dam completion. According to numerical simulations, only particles smaller than medium gravels (d