Abstract In the McMurdo Dry Valleys, Antarctica’s largest ice‐free area, the stream channels consist of rock and sediment that are underlain by permafrost. Substantial permafrost degradation and channel erosion occurred in January 2012 on the west branch of Crescent Stream, while the east branch remained unaffected. Long‐term stream water chemistry samples have been collected in Crescent Stream as part of the MCM LTER ecosystem monitoring. The concentrations of major ions and nutrients were significantly higher in the affected west branch than the unaffected east branch, and the average concentrations of ions, as well as nitrite and nitrate, were significantly greater in Crescent Stream after the 2012 degradation than before. Our results show that while a large disturbance event can increase solute inputs and shift the long‐term average dissolved ion concentrations, the overall stream discharge‐concentration relationship may remain chemostatic.