Colonel By Lake, located near Kingston, Ontario, was created in the early 19th century during the construction of the Rideau Canal waterway. Canal flooding inundated a large area of the Cataraqui River lowlands, submerging important pre-contact and colonial settlements. In order to gain a better understanding of the pre-canal environment and its archaeological setting, a systematic bathymetry and side-scan sonar survey was conducted over a 2-km2 area of Colonel By Lake. A 2-D digital bathymetric model (DBM) of the lake bottom was constructed and overlain with side-scan mosaics to map the paleogeography of the river flood plain. The data-fused sonar images clearly identify the submerged pre-canal topography, including the former Cataraqui River channel, relict meanders, tree stump fields, and bedrock uplands defining the valley sides. By comparing the DBM with landscapes depicted in pre-canal period maps (ca. 1828), the locations of several potential archaeological targets were identified. The DBM provides a basis for mapping submerged cultural resources in the Rideau and for predicting the location of undiscovered archaeological sites. The results show that integration of single-beam bathymetric mapping with side-scan imagery is an effective strategy for mapping submerged terrestrial landscapes and archaeological inventory in shallow water settings. © 2008 Wiley Periodicals, Inc.