As part of the Great Lakes Restoration Initiative (GLRI) project template 774-18 entitled “Development of monitoring and response methodologies, and implementation of an Adaptive Management Framework to work towards Eradication of Grass Carp in Lake Erie” an integrated bathymetric/hydrodynamic/water-quality survey of the Maumee River (Ohio) was completed by the U.S. Geological Survey (USGS) in the summer of 2019. These data were collected to inform the development of a one-dimensional hydraulic model and associated Fluvial Egg Drift Simulator (FluEgg) model of the Maumee River downstream from Defiance, Ohio. The data contained in this data release were collected by the USGS Ohio-Kentucky-Indiana Water Science Center to inform the development of these models by the USGS Central Midwest Water Science Center. The survey was completed over two periods of time: June 24–28, 2019, and July 29 to August 1, 2019. The first survey period concentrated on the reach between Grand Rapids, Ohio, and Lake Erie, while the second period concentrated on the reach between Defiance, Ohio, and Grand Rapids, Ohio. Survey data include bathymetry (depth and bed elevation), three-dimensional water velocity, discharge, and basic water-quality properties. A total of 251 cross sections were surveyed (141 upstream from and 110 downstream from Grand Rapids Dam, respectively) and data were also collected along streamwise transits between sections. Due to rapids, high-water, access, and safety concerns, no data were collected in the 23.9-kilometer reach downstream from the dam at Grand Rapids, Ohio. The upstream-most cross section is 280 meters downstream from the low-head dam approximately 6.6 kilometers downstream from Defiance, Ohio. The downstream-most cross section is located 290 meters downstream from the U.S. Coast Guard Station at Toledo, Ohio (3900 N Summit St, Toledo, Ohio, 43611). All data were collected by a manned survey vessel with a two-person survey crew of trained hydrographers. All data were georeferenced using a Trimble R10 Global Navigation Satellite System (GNSS) receiver mounted on the survey vessel and connected to the Ohio Department of Transportation (ODOT) real-time virtual reference station (VRS) network. This component of the data release consists of water velocity and water-quality data measured in the Maumee River between Defiance, Ohio, and the river mouth at Lake Erie at Toledo, Ohio. Velocity data were collected using a 1200 kilohertz Teledyne RD Instruments RiverPro acoustic Doppler current profiler (ADCP) deployed on a fixed mount from the survey vessel. The GNSS receiver was mounted directly above the ADCP. The sampling frequency varied slightly with the dynamic configuration of the ADCP but was generally between 1 to 2 Hertz. Data have been post-processed using the Velocity Mapping Toolbox v4.09 (VMT; Parsons and others, 2013) and its GIS Table Creation Utility with temporal averaging of 5 seconds. Both layer- and depth-averaged velocities are included in the data files and files are included for both the depth from surface (DFS) reference and height above bottom (HAB) reference. Layers are defined in 1-meter intervals for both references across the full water column and 0.5-meter intervals for points within 2 meters of the water surface or bottom. Water-quality data include two-dimensional, near-surface point measurements of basic water-quality properties in the Maumee River between Defiance, Ohio, and the river mouth at Lake Erie at Toledo, Ohio. Water-quality properties include temperature, specific conductance, pH, dissolved oxygen, turbidity, total chlorophyll, and phycocyanin concentration (the latter two properties were only collected upstream of Grand Rapids, Ohio). These data were collected using a Xylem EXO2 sonde (SN 16J103377) equipped with a temperature/conductivity sensor (SN 17A103858), pH sensor (SN 18G103338), optical dissolved oxygen sensor (SN 17A103549), turbidity sensor (SN 16K102514), total algae phycocyanin smart sensor (SN 12M100504), and central wiper. The sonde was deployed off the side of a manned survey vessel using a fixed mount at a depth of approximately 0.3 meters below the water surface. All properties were sampled at 2-second intervals as the vessel completed the survey (for both cross sections and streamwise profiles) and a 6-second moving average was applied in post-processing. References: Parsons, D.R., Jackson, P.R., Czuba, J.A., Engel, F.L., Rhoads, B.L., Oberg, K.A., Best, J.L., Mueller, D.S., Johnson, K.K. and Riley, J.D., 2013, Velocity Mapping Toolbox (VMT): a processing and visualization suite for moving-vessel ADCP measurements. Earth Surface Processes and Landforms, v. 38, no. 11, p. 1244-1260. [Also available at https://doi.org/10.1002/esp.3367.]