Bark beetle outbreaks have impacted over 58 million acres of coniferous forest in the Western US since 2000, an area slightly larger than the state of Utah. Most of these beetle-impacted forests are in semi-arid, snow-dominated headwater catchments that generate a disproportionate fraction of water supplies. Limited previous studies have shown severe beetle-kill can cause mixed increases and decreases in streamflow. This study is the first to empirically explore changes in streamflow following a recent spruce beetle outbreak in southwest Colorado using a paired catchment approach. The period following beetle kill (2014-2019) was 0.95° C warmer and 5.8 cm/year drier than the 21-year period prior to the disturbance’s peak (1993-2013). There was no change in streamflow in the control basins after beetle kill. In contrast, post-beetle kill had 34% higher peak flows on average and consistent predictions of >14% increases in streamflow in wetter basins and >20% in drier basins. Our results suggest that higher streamflows are primarily driven by 44% higher runoff efficiencies during the snowmelt period. The increased flows due to beetle kill are occurring at a time when control catchments have unchanged runoff efficiencies. These findings are the first to clearly show streamflow increases following extensive spruce beetle kill in watersheds that contribute water to millions of downstream residents. Moreover, our findings contrast with evidence of unchanged or decreased streamflow following mountain pine beetle kill in nearby parts of Colorado, highlighting the need for better post-disturbance hydrologic predictions in these important montane forests.