Wild, scenic, and toxic: Recent degradation of an iconic Arctic watershed with permafrost thaw

The Salmon River is among the most remote and protected watersheds in North America. Its pristine wilderness was featured in the opening chapter of John McPhee’s nonfiction classic, “Coming into the Country”. In 2019, the gin-clear waters of the Salmon turned orange and have remained turbid and discolored since. The sudden degradation of the Salmon and many other formerly clear streams in the region is thought to reflect sulfide mineral weathering following permafrost thaw. Here, we show the Salmon River mainstem and most of its tributaries have metal concentrations deemed toxic to aquatic life. Our findings might help explain a recent crash in chum salmon returns, which are an important commercial and subsistence resource in an economically challenged region.