Recent efforts to model spring breeding habitats of fish in the St. Lawrence have revealed significant gaps in land use descriptions for the floodplains of Lac Saint-Pierre. In order to fill these gaps, aerial photographs taken in 1950, 1964 and 1997 were assembled in mosaic fashion and then digitized, georeferenced and interpreted to categorize 28 fish habitat classes. For each of the three periods, interpretation made it possible to categorize and georeference polygons (e.g. wet meadows, perennial crops) and linear elements (e.g. windbreaks, riparian strips, roads) and to compile these with their properties (habitat class, length, perimeter, surface area). To facilitate and refine subsequent analyses, all polygons and linear elements were delineated with the aid of several layers of information, including the boundaries of regional county municipalities, drainage basins, several flood scenarios, and three large units: the north and south shores of Lac Saint-Pierre and the Sorel archipelago. This report describes the methods used and the constraints encountered; it also presents certain interpretation limits and a summary analysis of habitat classes in the three periods studied. A temporal trend analysis of habitat dynamics in the three periods has yet to be completed. Source files containing the data have been published and are available to anyone interested in land use in the floodplains of Lac Saint-Pierre or wishing to extend the study of changes in these landscapes and habitats over the past fifty years, depending on their field of interest (e.g. fish habitats, waterfowl nesting, agricultural landscape).