Exceptionally low river flows across Europe in July 2026 disrupted navigation, energy production and water-dependent economic activity. Using near-real-time, circulation-constrained global climate storylines combined with regional hydrological simulations, we show that nearly half of the European rivers analysed experienced discharge reductions exceeding 50% relative to the 1980-2025 July climatology. We find a widespread anthropogenic fingerprint on July 2026 low flows, with human-induced climate warming reducing discharge, by 26-38% at downstream locations along major European rivers including Rhine, Rhone, Po, and Danube. These reductions were largely driven by reduced spring-to-summer precipitation combined with enhanced evapotranspiration, intensifying the low-flow conditions associated with the observed circulation pattern. Our forensic investigation demonstrates that anthropogenic warming is already reshaping societally consequential low-flow extremes across Europe, reinforcing the need to accelerate water resilience and preparedness in a warming climate.