Peatlands host ecosystems of high ecological value and play essential hydrogeochemical roles within watersheds. These sensitive environments are particularly abundant in northwestern Quebec, where mining activities are expanding. Nevertheless, the hydrogeochemical impacts of mine dewatering on peatlands remain poorly understood, limiting the ability to adequately assess the environmental consequences of mining operations. In this context, this study evaluates the hydrogeochemical effects of dewatering on a peatland located adjacent to the Akasaba West open-pit mine in Abitibi–Témiscamingue (QC, Canada). The site was instrumented with 18 piezometers arranged in six clusters, recording water pressure at one-hour intervals since 2019. Measurements began prior to mine development and continued throughout operations, enabling real-time assessment of hydrological responses to dewatering. Seasonal sampling campaigns conducted before and during dewatering were used to characterize changes in peat pore water chemistry. Laboratory ultrafiltration experiments were performed to evaluate the role of colloids in controlling the mobility of metals and metalloids in peat porewaters. A coupled numerical model was developed using SEEP/W and CTRAN/W to simulate groundwater flow and dissolved mass transport under both natural and dewatering-affected conditions. The results provide new insights into the hydrological and hydrogeochemical responses of peatland systems to mining-induced perturbations and contribute to improving environmental management of peatlands in mining regions.