Floodplain wetlands are among the most productive components of large river ecosystems, yet regulation, leveeing, and nutrient retention in reservoirs have left many rivers nutrient-poor and hydrologically disconnected from their floodplains. In the lower Kootenai River (Idaho, USA), an oligotrophic, regulated system managed in part through nutrient supplementation, reestablishing seasonal connectivity to off-channel habitats is a key restoration strategy for providing food resources to higher tropic levels. We evaluated how reconnection projects influence water quality and lower-trophic level standing stock by comparing river (mainstem), connector-channels, and interior wetland/pond habitats across seasons and hydrologic conditions from 2018-2024. During pre-connection periods and during hydrologic connection windows, we quantified water chemistry (N, P, C), chlorophyll-a, phytoplankton density, and zooplankton density. The wetland/pond had elevated nutrient concentrations, chlorophyll-a, and plankton densities. During connection windows, connector channels exhibited intermediate to enriched conditions relative to the mainstem river, indicating the mobilization and export of wetland-derived nutrients and plankton to the mainstem during reconnection. These patterns support a process-based mechanism in which reconnected floodplain wetlands accumulate biomass and nutrients under baseflow and export high-quality subsidies to connector channels and the mainstem river during inundation and drawdown. Our results demonstrate that targeted floodplain reconnection can restore productive wetland habitats that act both as biodiversity and productivity hotspots and as dynamic sources of nutrient and plankton subsidies to nutrient-limited mainstem rivers. Wetland reconnection can complement nutrient-addition programs to enhance food resource availability and resilience in large, oligotrophic rivers. These productive wetlands may also provide high-quality food resources for higher consumers, including waterfowl, linking river restoration to broader floodplain and wildlife benefits.