The widespread presence of obsolete or unsafe dams highlights the need for effective restoration strategies. This study examines the effects of dam removal on organic matter decomposition in a mountainous Mediterranean stream using the cotton-strip technique. We compared this function among three reaches: one where a dam was removed (restored), one with an intact dam (impacted), and one in natural conditions (reference). Seasonal sampling was conducted over four campaigns. Analysis of variance revealed a statistically significant effect of stream reach on tensile loss. Non-temperature-corrected rates in the restored reach (3.05 ± 0.83) were similar to those in the reference reach (3.22 ± 0.75) (p = 0.47) and higher than those in the impacted reach (2.37 ± 0.96% d-1) (p <0.0001). Greater current velocities and reaeration coefficients were measured in our restored and reference reaches. In addition, lower current velocities increase sedimentation, creating more suitable environments for biofilm overgrowth which can eventually prevent light from reaching the benthic communities and increase heterotrophic activity. This also could explain the lowest tensile loss rates obtained in the impacted reach, especially closer to the dam. However, when rates were corrected by water temperature, tensile losses in the restored reach (0.24 ± 0.05) were higher than those in the impacted reach (0.20 ± 0.08) (p = 0.0086) and lower than those in the reference reach (0.29 ± 0.06% dd-1) (p = 0.0013). These findings indicate that organic matter decomposition was fastest in the least disturbed environment and that, while dam removal improved decomposition rates, they did not fully recover to reference conditions. A possible explanation is that insufficient time has elapsed since restoration. Further improvements in stream channel geomorphology and recolonization by flora and fauna are expected over time. These insights are critical for informing future dam removal restoration projects.