Purpose and scope: The purpose of this report is to quantify the base flow of 19 continuously gaged Long Island streams during 1960-75, which includes the 1962-66 drought. These base-flow data will be used in calibrating computer models designed to predict the response of Long Island streams to hydrologic stresses such as the lowering of ground-water levels in response to large-scale sanitary sewering. The data will also be used to assess the long-term impact expected to result from storm- and sanitary-sewer systems on base flow of streams.