Windermere is a glacially overdeepened lake located in the southeastern Lake District, UK. Using the three-dimensional (3D) Chirp subbottom profiler, we image mass movement deposits related to the Younger Dryas (YD) within a decimetre-resolution 3D seismic volume, documenting their internal structure and interaction with preexisting deposits in unprecedented detail. Three distinct flow events are identified and mapped throughout the 3D survey area. Package structures and seismic attributes classify them as: a small (total volume of c. 1500 m3) debris flow containing deformed translated blocks; a large (inferred total volume of c. 500,000 m3), homogeneous fine-grained mass flow deposit; and a debris flow (inferred total volume of c. 60,000 m3) containing small (c. 8.0 × 2.0 m) deformed translated blocks. Geomorphological mapping of their distribution and interaction with preexisting sediments permit the reconstruction of a depositional history for the stratigraphic units identified in the seismic volume.