In 2016, the U.S. Army Corps of Engineers (USACE) started collecting high-resolution multibeam echosounder (MBES) data on Lake Koocanusa. The survey originated near the International Boundary (River Mile (RM) 271.0) and extended down the reservoir, hereinafter referred to as downstream, about 1.4 miles downstream of the Montana 37 Highway Bridge near Boulder Creek (about RM 253). USACE continued the survey in 2017, completing a reach that extended from about RM 253 downstream to near Tweed Creek (RM 244.5). In 2018, the U.S. Geological Survey (USGS) Idaho Water Science Center completed the remaining portion of the reservoir from RM 244.5 downstream to Libby Dam (RM 219.9). The MBES data collected in 2016 and 2017 by the USACE was combined with the MBES data collected in 2018 by the USGS. The USGS also developed an elevation-area-capacity table at one-foot intervals from the minimum pool elevation (2,290.84 ft) to the maximum pool elevation (2462.84 ft) using the new bathymetry data. The updated stage-capacity table will be compared to the current usable storage estimate of 4,979,500 acre-feet and published in a USGS Scientific Investigations Report. A 10-ft digital elevation model (DEM) and minimum and maximum pool contours also were generated from the bathymetric data and are provided in this data release.