In 2012, Hurricane Sandy created an open breach in the barrier island system along the south shore of Long Island, N.Y. This breach formed at a location known as Old Inlet and migrated rapidly westward over the winter storm season following Hurricane Sandy. On May 14, 2015, U.S. Geological Survey (USGS) New York Water Science Center (NYWSC) personnel collected data to evaluate channel geometry, water velocity, and discharge of an open breach in the Federal Wilderness area of Fire Island National Seashore, N.Y. The breach resulted from major coastal flooding and overwash created by Hurricane Sandy on October 29, 2012. Data were collected using a Sontek M9 Acoustic Doppler Current Profiler (ADCP) with Real-Time Kinematic (RTK) Global Positioning System (GPS). Data were processed using a Geographic Information System (GIS) for interpolation and display. An initial series of transects was collected starting about 4 hours before ocean low tide on May 14, 2015. Data were collected perpendicular to flow through the breach beginning at 0725 Eastern Standard Time (EST) and ending at 0811 EST. The first set of transects was taken near the bayward side of the breach, with subsequent sets collected progressively closer to the seaward side of the breach. Discharge ranged from 16,400 cfs (cubic feet per second) during the beginning set of transects to 17,400 cfs during the second set of transects. A second series of transects was collected starting about 4 hours before ocean high tide on May 14, 2015. Data collection began at 1335 EST and ended at 1445 EST. The first set of transects was taken perpendicular to the flood tidal channels bayward of the former Great South Bay (GSB) shoreline; subsequent sets were collected progressively closer to the seaward side of the breach. Discharge ranged from 16,500 cfs during the beginning set of transects to 24,900 cfs during the final set of transects. Additional data were collected along the approximate centerline and adjacent to the shores of the channel to map the inundated area of the breach. The overall mapped area includes data collected during discharge measurements of both incoming and outgoing tide conditions.