This data release contains results of a high-water mark survey across the five boroughs of New York City following flash flooding caused by the remnants of Hurricane Ida, September 1, 2021. The survey was conducted between September 7 and November 23, 2021, and is based on observations of mud, debris, and seed lines left by the flooding. Real time and static GNSS surveying as well as available lidar data were used to determine high-water mark elevations at 83 locations. Additional data associated with Hurricane Ida flooding can be found in the USGS Flood Event Viewer, https://stn.wim.usgs.gov/fev/#2021Ida