Documenting the Impacts of Thermal Effluent on Downstream Ice Formation on the Chena River During a Record Cold Winter in Fairbanks, Alaska

Abstract

Most Interior Alaska rivers develop seasonal ice cover through the winter, providing important ecosystem and societal services. A longstanding exception commonly occurs on the Chena River as it flows through the City of Fairbanks, primarily attributed to power-plant effluent that causes ice-free conditions far downstream. Over the winter of 2025–2026, we sought to document the extent of downstream open water in this urban river relative to hydrologic and weather conditions. A combination of satellite imagery and time-lapse cameras show that ice began forming in late October with near complete ice-cover upstream of the discharge zone by early December and open water persisting far downstream (6 km) through most, if not all of, the entire winter. Sensors placed upstream and incrementally downstream of the discharge zone detected water temperatures at 0 °C above and far below (12 km) all winter long, but 200 m downstream averaged 0.8 °C and 1100 m downstream averaged 0.3 °C. Estimated cooling lengths to return to near-freezing temperatures downstream from the power plant were approximately 9 km based on observed water temperature data. Notably, the winter of 2025–2026 ended up being the coldest in Fairbanks history dating back 96 years, despite a long-term trend towards warmer winters. This striking winter context is considered relative to power-plant operations, downstream impacts on freezing, and sources of natural and human-influenced winter open-water occurrence on other northern rivers.