Water supply lakes are the primary source of water for many communities in northern and western Missouri. Therefore, accurate and up-to-date estimates of lake capacity are important for managing and predicting adequate water supply. Many of the water supply lakes in Missouri were previously surveyed by the U.S. Geological Survey in the early 2000s (Richards, 2013) and in 2013 (Huizinga, 2014); however, years of potential sedimentation may have resulted in reduced water storage capacity. Periodic bathymetric surveys are useful to update the area/capacity table and to determine changes in the bathymetric surface. Monroe Lake B (locally known as Monroe City South) is a water supply lake used by the city of Monroe City in northeastern Missouri. The surface area of Monroe Lake B is about 61.9 acres at the full pool level of the primary spillway (712.8 feet above the North American Vertical Datum of 1988). No previous bathymetric survey has been completed at this lake. In April 2021, the U.S. Geological Survey, in cooperation with the Missouri Department of Natural Resources and in collaboration with the City of Monroe City, completed a bathymetric survey of Monroe Lake B using a multibeam echosounder. The water-surface elevation during the survey was about 712.8 feet. The echosounder data can be combined with light detection and ranging (lidar) data to prepare a bathymetric map and a surface area and capacity table for the lake. The gridded bathymetric point data (MonroeCitySouth2021_bathy_pts.zip) were computed on a 1.64-foot (0.50-meter) grid using the Combined Uncertainty and Bathymetry Estimator (CUBE) method, which is used as the source of points to create the bathymetric surface. Bathymetric quality-assurance data (MonroeCitySouth2021_QA_raw.zip) were collected to evaluate the vertical accuracy of the gridded bathymetric point data. Each of these two zip files contains a shapefile with an attribute table. Attribute/column labels of each table are described in the "Entity and attribute" section of the metadata file. References Cited: Huizinga, R.J., 2014, Bathymetric surveys and area/capacity tables of water-supply reservoirs for the city of Cameron, Missouri, July 2013: U.S. Geological Survey Open-File Report 2014–1005, 15 p., http://dx.doi.org/10.3133/ofr20141005. Richards, J.M., 2013, Bathymetric surveys of selected lakes in Missouri—2000–2008: U.S. Geological Survey Open-File Report 2013–1101, 9 p. with appendix, http://pubs.usgs.gov/of/2013/1101.