Nearly 30 taxa of Pleistocene freshwater snails and sphaeriids have been found in recent years at eight localities in glacial Lake Iroquois deposits. Older reports of molluscs from Lake Iroquois deposits by Ami (1900) and Coleman (1899, 1933) probably represent confusion with shells from Lake Algonquin and Wisconsinan interstadial deposits at Toronto.Molluscs are most abundant in shallow-water sediments deposited in former lagoons and near former river mouths in Lake Iroquois. A northeastward limit of occurrences near Oshawa, Ontario may reflect the influence of the retreating ice-margin in eastern Ontario 12 000 years ago. Shells have been found occasionally in deposits of lower level, post-Iroquois (but pre-Champlain Sea) lake stages in eastern Ontario. The Lake Iroquois fauna suggests the presence of vegetation both on land and in the water with water conditions at individual sites varying from oligotrophic to eutrophic.