The U.S Geological Survey conducted hydrographic surveys from July 23-25, 2018 to monitor fish spawning substrate placements (reefs) in the Detroit and St. Clair Rivers, Michigan. A multibeam echosounder was used from the Great Lakes Science Center research vessel Cisco to collect hydrographic data. These data were used to generate maps of river bottom topography in locations where spawning substrates have been placed. Reefs that had been constructed at the time of survey in the Detroit River included: Fighting Island, Fort Wayne, New (East) Belle Isle, Belle Isle, and Grassy Island. The reefs constructed in the St. Clair River at the time of survey included: Middle Channel, Pointe aux Chenes, and Harts Light.