Permanently frozen ground – permafrost – is a defining characteristic of the Arctic.  However, climate warming is thawing permafrost in many areas, leading to failures in soil structure called thermokarsts.  In the foothills of the Brooks Range, Alaska, thermokarsts have been observed to deliver substantial quantities of sediments to lakes and streams.  We have quantified significantly increased sediment and nutrient loading from thermokarsts to streams in two well-studied locations: the Toolik Lake Natural Research Area and the Feniak Lake area within the Noatak River Preserve (National Park Service).  Although quantitative historical data are scarce, we now have substantial evidence from our Feniak Lake research site that thermokarst activity has increased significantly in the last 25-30 years.  Our previous research in Arctic streams has shown that even minor increases in nutrient loading stimulate primary and secondary production. However, the massive increase in sediment loading could smother benthic communities and negate the impacts of increased nutrient delivery. Although the terrestrial area impacted by thermokarsts is limited, the aquatic habitat altered by these failures can be extensive. Warming in the Arctic foothills appears to be accelerating thermokarst formation which may have substantial and wide-spread impacts on arctic stream ecosystems.