Arctic headwater streams play a crucial role in the carbon cycle, contributing disproportionately to carbon dioxide (CO₂) evasion despite their small size and surface area. In this study, we examined how seasonal hydrologic patterns, such as spring snowmelt (freshet), mid-summer low-flows (baseflow) and the late summer period in August and early September (late-season), influence CO₂evasion in Arctic headwater streams (1–9 km²basin size; 1–4 stream orders) near Utqiagvik, Alaska. During three summers, we measured key environmental parameters (CO₂partial pressure, water temperature, discharge, dissolved organic carbon (DOC), gas transfer velocity) and CO₂evasion using a floating chamber. CO₂evasion followed distinct seasonal patterns with the highest evasion rates during freshet, followed by the late-season, and the lowest during baseflow. Despite its short duration (10 d), freshet accounted for 22% more total CO₂evasion than the 36 d late-season period. The descending peakflow within freshet had the highest median evasion rate (2486 mg C–CO₂m⁻²d⁻¹) of the entire season, while the ascending portion of the peakflow had the lowest (448 mg C–CO₂m⁻²d⁻¹). These two freshet periods showed a statistically significant difference (p< 0.05). Water temperature, DOC, andpCO₂explained 35%, 30% and 67% of freshet evasion variability, respectively. No measured parameters reliably predicted CO₂evasion for the baseflow or late-season periods, suggesting increased hydrologic and biological complexity. The stream showed supply-limitation during freshet but transitioned to chemostatic behavior thereafter. By synthesizing our measurements with previously published data, we show that small streams (<1 km²watersheds) exhibit ∼10-times the CO₂evasion rates than large waterways (>1000 km²). We also find that across the Arctic, only ∼15% of riverine CO₂measurements capture the freshet period. Together, the omission of small streams and the underrepresentation of freshet likely lead to a systematic underestimation of CO₂losses from Arctic surface waters to the atmosphere.