In order to investigate the bottom conditions existing along a transect of the St. Lawrence River, where it flows out of Lake Ontario, sediments were collected at two depths by scuba divers. The samples were analyzed using soil chemical, physical, and mineralogical methods.The medium to fine silt fraction dominates the non-acid treated samples, while the action of HCl increases the clay content some ten times. Although Ca is the dominant exchange cation exchangeable Mn is unusually high, perhaps reflecting the presence of manganiferous shales in the watershed. Dissolved Ca is the dominant cation in the sediment waters but the high Na is probably derived from the Canadian Shield element in the surrounding lithoiogy. Semi-quantitative clay mineralogy suggests that illite and illite–chlorite interstratifications are most common while the absence of montmorillonite, a common constituent of Podzol A2 horizons, is noteworthy.