Within the Hudson and James Bay (HJB) Lowlands, one of the world’s largest contiguous peatlands, interest in mining development has led to concerns about downstream impacts propagating to riverine and coastal ecosystems, which are already responding to effects of climate change. The southwestern Hudson Bay and western James Bay coastline, part of the homeland of Omushkego Cree, is a crucial habitat for birds, fish and marine mammals. This work seeks to quantify delivery of nutrients and land-derived carbon from HJB rivers to the coast and explore the seasonal and spatial variability as part of building a baseline for Cree-led monitoring and long-term stewardship initiatives in the region. Here, we present preliminary results of community-partnered river and coastal water quality monitoring carried out over 2023-2025 with Moose Cree First Nation and Weenusk First Nation to study, respectively, the Moose River and Winisk River coastal areas. Specifically, the evolution of water chemistry (pH, dissolved inorganic carbon and alkalinity), nutrient concentrations, and dissolved organic carbon is described across the freshwater to marine transition in the Winisk River estuary during summer and compare the results to other HJB coastal areas that have been studied more thoroughly, including the Moose River and coastal areas of eastern James Bay. We further discuss next steps to build a baseline dataset suitable for detecting impacts of changes in the watersheds and address local monitoring objectives and research priorities.