This polyline shapefile consists of digital contours that represent the potentiometric-surface altitude of water in the Lloyd and contiguous North Shore aquifer beneath Nassau and Suffolk Counties, Long Island, New York. The U.S. Geological Survey constructed a potentiometric-surface altitude map using ground-water levels measured in the Lloyd and North Shore aquifers during the spring of 2016. Contours were constructed at a scale of 1:125,000 from water-level data collected at 60 groundwater monitoring wells. The potentiometric-surface altitude contours were digitized and compared to 1997, 2006, 2010 and 2013 potentiometric-surface altitude maps. The contours range from -5 to 60 feet at 5 foot intervals above and below the National Geodetic Vertical Datum of 1929. This polyline shapefile is a digital representation of the potentiometric-surface contours presented in sheet 3 of Scientific Investigations Map 3398.