Wildfires alter terrestrial subsidies to rivers, but the effects of wildfire subsidies on ecosystem metabolism (gross primary production, GPP and ecosystem respiration, ER) and dissolved O2 are not well known due to a paucity of monitoring during and after wildfires. In July and August 2022, the McKinney Fire burned 240 km2 in Northern California along the Klamath River and caused a series of debris flows when heavy rains fell on the active wildfire. We examined the impacts of this high-severity wildfire on GPP, ER, and dissolved O2 by comparing the immediate (days) and mid-term (17 mo) post-fire metabolic fluxes to the 4.5 y preceding the wildfire. While the initial sediment pulse briefly turned the river anoxic, due in part to extremely high fluxes of ER (< -60 g O2 m-2 d-1), low dissolved O2 concentrations lasted <1 d. Following the wildfire, turbidity remained elevated over background levels for the duration of the study, causing lower post-fire fluxes of GPP (mean GPP = 8.7 and 3.3 g O2 m-2 d-1 before and after the fire, respectively). While net ecosystem production decreased following the fire (mean NEP = 1.7 and -0.4 g O2 m-2 d-1 before and after the fire, respectively), ER continued to reflect GPP on most days, causing lower fluxes of ER after the initial debris flow. Despite more negative NEP, the coupled reductions in GPP and ER after the fire caused less daily variation in dissolved O2, resulting in fewer days of minimum daily dissolved O2 falling below the management target of 90% saturation. While wildfire associated debris flows can have short-term catastrophic effects on water quality, including anoxia leading to fish kills, moderate increases in turbidity may benefit dissolved O2 where high fluxes of GPP cause water quality impairment. Long-term data that includes pre-disturbance baselines are needed to detect these changes to ecosystem function and water quality that could otherwise go unnoticed.