Boreal peatlands and the streams that drain them are acidic, carbon-rich, and nutrient-poor ecosystems that are vulnerable to climate change. We investigated how climate change affects peatland stream chemistry through the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. SPRUCE is an ecosystem-scale manipulation designed to examine the effects of warming (+0, +2.25, +4.5, +6.75, +9°C) and elevated CO2 (+500 ppm) over a 10-year period in an ombrotrophic bog in northern Minnesota (USA). The experimental design includes ten 12-m diameter, 8-m tall enclosures with warming both above and belowground. A belowground corral hydrologically isolates each plot, and an outflow system allows for lateral, passive drainage of water akin to stream flow. Automated samplers collect flow-weighted water samples from each outflow, and samples are retrieved weekly and analyzed for total organic carbon (TOC), inorganic and total nutrients, anions, cations, metals, and pH. After 7 years of warming, several changes in stream chemistry were observed. Notably, TOC concentrations increased with warming, from 52 mg/L on average at the +0°C enclosures to 87 mg/L at the +9°C enclosures, likely due to warming-induced increases in peat mineralization and leaching of recently produced photosynthate. Several other solutes exhibited similar increases (i.e., calcium, magnesium) including those that form complexes with TOC (i.e., aluminum, iron). In contrast, the response of nutrients to warming has been muted, possibly because of rapid uptake of mineralized nutrients by plants and microorganisms in this nutrient-limited ecosystem. Findings to date suggest that climate change may alter the chemistry of stream water flowing from peatlands, the effects of which may cascade to downstream environments.