The breeding colony of the Double-crested Cormorant (Phalacrocorax auritus) on East Sand Island in the Columbia River estuary has grown dramatically over the last 13 years, in contrast to declines at other colonies along the coast of the Pacific Northwest. Immigration from other colonies has occurred and the East Sand Island colony is now the largest for the species on the Pacific coast of North America. Despite substantial increases in the size of the East Sand Island colony, overall numbers of the West Coast subspecies (P. a. albociliatus) appear to be slowly increasing relative to the interior population (P. a. auritus). Based on the most recent regional population data available, a conservative estimate indicates that the colony on East Sand Island represents over 30% of P. a. albociliatus breeding adults. We advocate that the subspecies P. a. albociliatus be considered a distinct population segment and managed according to overall population size and trends for this subspecies.