A new report by a public policy think tank says low water levels in the Great Lakes and St. Lawrence River could result in severe economic fallout for the region.

The Mowat Centre study says it could cost the United States and Canada more than $19 billion by 2050 if water levels remain low.

The report says water levels in the Great Lakes and St. Lawrence basin "fell dramatically" in 1997-98.

Since then, it says much of the basin has experienced the longest extended period of lower water levels since the two countries began tracking levels in 1918.

The report adds that while water levels have "rebounded" since 2013, due to factors including cooler temperatures in winter, it's "unclear" if this is the beginning of a trend.

The Great Lakes — which hold about 20 per cent of the world's surface freshwater supply — are also home to industries including hydroelectricity and commercial shipping, as well as recreational boating and fishing.