The continuous lowering of Lake Michigan-Huron levels has caused increasing concerns. St. Clair River, which drains Lakes Michigan and Huron to Lake St. Clair-Lake Erie, appears to bear much of the blame. The three most possible causes are the erosion of the St. Clair River bed, relative change in net basin supply (NBS), and differential glacial rebound. Dredging and erosion so induced might have changed the river conveyance. In this paper, only sediment erosion will be considered. Among many other things, sand/gravel mining, sediment supply into the St. Clair River, and changes of the river cross section at some critical points may have affected the conveyance. In this study, a two-dimensional numerical code, HydroSed2D, will be used to investigate whether the St. Clair River is still eroding under current flow conditions. HydroSed2D is a two-dimensional depth-averaged hydrodynamic code with a sediment transport module. It is based on the shallow water equations. This code has been used in many engineering applications. Bathymetry data is compiled from different sources (single beam and multi-beam echo sound surveys). Sediment size distribution information is from the image analysis of under water videos. With the bed shear stresses results, the possibility of sediment movement in the St. Clair River is analyzed.