This map shows the extent of tributary habitat that is downstream of the first barrier and is accessible by fishes that migrate between Lake Ontario and its tributaries. Data on tributary habitat downstream of barriers in Ontario streams and rivers were available from Ontario Ministry of Natural Resources in the Aquatic Landscape Information System (ALIS). Comparable data on migration barriers in for Lake Ontario tributary streams and rivers in New York were part of a stream habitat fragmentation model developed by Cornell University (Meixler et al 2003). Data were not available for the St. Lawrence tributaries in Ontario or New York; if possible, those data will be added to a future version of this map.