The erosion and active transport of legacy mine tailings (called “stamp sands”) are impacting native fish species and aquatic habitats on a shallow water rocky reef complex along the Keweenaw Peninsula of Michigan called Buffalo Reef. Stamp sands are spreading from an old mill site at the Town of Gay and settling on the reef. Multiple surveys have documented the underwater migration of toxic, metal-rich stamp sands and progressive burial of areas of hard/complex lakefloor, such as cobble fields. The finer-grained, muddy fraction of the mine tailings has been winnowed by waves and currents and transported to unknown locations in deeper waters offshore. High-resolution geophysical mapping of the bay in 2018 revealed a complex pattern of sandy bedforms on the lakefloor and a general trend of decreasing sediment thickness in areas more distal from the original source, suggesting a flux of sandy sediment from NE to SW across the bay. The present study used multi-beam echosounders deployed in August 2021 to update the high-resolution bathymetry and acoustic backscatter maps with the intent to document sand migration, and to describe habitat geomorphology and substrate variation.