These data are high-resolution bathymetry (riverbed elevation) in LAS format, generated from the August 1-3, 2022, hydrographic survey of the Calumet River and Calumet Sag Channel in Cook County, Illinois. The survey extends from the junction with Lake Michigan in the northeast downstream to the junction with the Chicago Sanitary and Ship Canal in the southwest. Hydrographic data were collected using a high-resolution multibeam echosounder mapping system (MBMS), which consists of a multibeam echosounder (MBES) and an inertial navigation system (INS) mounted on a marine survey vessel. Data were collected as the vessel traversed the channel along overlapping longitudinal survey lines distributed throughout the reach. Data collection software integrated and stored the depth data from the MBES and the horizontal and vertical position and attitude data of the vessel from the INS in real time. Data processing required specialized computer software to extract bathymetry data from the raw data files and to summarize and map the information. The bathymetry dataset is provided in American Society for Photogrammetry and Remote Sensing (ASPRS) LAS format with metadata as CalSagChannel_bathymetry_2022-08.las. The LAS format is a standardized binary format for storing 3-dimensional point cloud data and point attributes along with header information and variable length records specific to the data. Data points are stored as a 3-dimensional data cloud as a series of x (longitude), y (latitude), and z (elevation) points. Please refer to http://www.asprs.org/Committee-General/LASer-LAS-File-Format-Exchange-Activities.html for additional information.