The Canadian Hydrographic Service
Hourly water levels for Lake Ontario and the St. Lawrence River
Great Lakes Levels Home Page
1, 2 & 3 month levels, forecasts, bi-monthly connecting channel forecasts (including the St. Lawrence River) from the U.S. Army Corps of Engineers.
International St. Lawrence River Board of Control
Daily (posted weekly late Thursdays or Fridays) levels for Lake Ontario and St. Lawrence River down to Sorel. Daily outflows & upcoming weekly outflows.
Great Lakes Basin Hydrology
Monthly precipitation for each of the Great Lakes & total basin.
Monthly supplies and outflows for each of the Lakes.
International Joint Commission home page.