Extensive new data from previously unstudied Siberian streams and rivers suggest that mobilization of currently frozen, high‐latitude soil carbon is likely over the next century in response to predicted Arctic warming. We present dissolved organic carbon (DOC) measurements from ninety‐six watersheds in West Siberia, a region that contains the world's largest stores of peat carbon, exports massive volumes of freshwater and DOC to the Arctic Ocean, and is warming faster than the Arctic as a whole. The sample sites span ∼10⁶ km² over a large climatic gradient (∼55–68°N), providing data on a much broader spatial scale than previous studies and for the first time explicitly examining stream DOC in permafrost peatland environments. Our results show that cold, permafrost‐influenced watersheds release little DOC to streams, regardless of the extent of peatland cover. However, we find considerably higher …