Worldwide, numerous dams are aging and will either need to be replaced or removed within the next few decades. Little is understood about the fate of the carbon stored in these sediments that become soil when a dam is removed and a reservoir is drained. This study assessed the pool of carbon in the sediments of the former Lake Mills and Lake Aldwell of the Elwha River. Carbon storage was mapped spatially and by depth to 1m. Sediment carbon was also compared with forest soil carbon from glacial lake sediments. This dam removal project, the largest-known of its kind, can provide important information regarding the fate of carbon in sediment pools and fluxes when reservoir sediments become soil.