Found 2 places
Latitude: 38.8691 (38°52′9″N), Longitude: -90.1507 (90°9′3″W)
Site: mvs.usace.army.mil/navigation1/melvin%20lock
Latitude: 38.9184 (38°55′6″N), Longitude: -90.0918 (90°5′30″W)