A bathymetric dataset was collected on September 7, 2022, of Lost Lake (reservoir) located in the Modoc National Forest, California. Both bathymetric and terrestrial lidar (light detection and ranging) data were collected via a boat-based multibeam echosounder and lidar scanner to compute a digital elevation map (DEM) of the lakebed and the near shore. The DEM was used to provide an update to the stage-storage and stage-area relationships. Macrophyte growth in the shallow depths of the lake created erroneous data soundings. Removal of the erroneous data led to near-complete coverage and the surface was interpolated using the Topo to Raster tool in ArcGIS Pro. A U.S. Geological Survey (USGS) 3D Elevation Program (3DEP) lidar dataset collected in 2022 was used to merge the bathymetric and lidar data to create a complete DEM. Quality control of elevation survey data were compared to Global Navigation Satellite System (GNSS) fast static points collected on the same day. The lidar data has an average vertical difference of less than 0.05 meters (m) and bathymetry data had an average difference of 0.12 m compared to the fast static elevation points. The lowest spillway elevation was recorded at 7291.6 feet (ft) or 2222.48 m North American Vertical Datum of 1988 (NAVD88) and the dam crest elevation was recorded at 7296.6 ft or 2223.99 m NAVD88. Volumetric storage and surface area analysis was conducted on the DEM dataset at a 0.02 m vertical increments using the Storage Capacity tool in ArcGIS Pro. The storage at the lowest elevation of the spillway was 197.1 acre-feet (ac-ft) or 243,139 cubic meters (m³) with a surface area of 16.8 acres (ac) or 68,183 square meters (m²). The storage at the crest elevation was 288.6 ac-ft or 355,942 m³ with a surface area of 20.0 ac or 81,142 m².
