TORONTO -- Low water levels in the Great Lakes and St. Lawrence River could result in severe economic fallout for the region, totalling more than US$18 billion (C$19.3 billion) by 2050, according to a new report.

The report, released Thursday by the Mowat Centre and Council of the Great Lakes Region, said water levels in the Great Lakes and St. Lawrence basin "fell dramatically" in 1997-98.

Since then, the basin has experienced the longest extended period of lower water levels since the U.S. and Canada began tracking levels in 1918.

Mark Fisher, who heads the council, said there's a "very real future" where the region could be plagued by low-water trends.

"When you look at the last 13 years, we've gone through the longest period of low water levels in our history," he said.

Lake Michigan-Huron had the lowest water level ever recorded for the lake in January 2013.

The economic footprint of the Great Lakes Region is US$4.9 trillion (C$5.25 trillion), or around 28 per cent of combined Canadian and U.S. economic activity.

The report said lower water levels in the Great Lakes -- which hold about 20 per cent of the world's surface freshwater supply -- would impact industries including hydroelectricity and commercial shipping, as well as recreational boating and fishing and property values near the shores.

It added 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 general rule is that there is more evaporation and less precipitation, so less water in the system," Fisher said, explaining that only one per cent of the waters of the Great Lakes are renewed on an annual basis by precipitation.

He added that the study's projections are "conservative," given that researchers did not look at indirect effects or how low water levels could impact human health, commercial fishing or the manufacturing sector.

"The costs would only get much larger if we calculated in the indirect costs," he said.

Climate change is a closely related issue and requires input on local, provincial and federal levels, Fisher said, adding that U.S.-Canada collaboration will be essential to safeguard the future of the Great Lakes.

"The challenge that people have is (climate change) is gradual, it's incremental, it's hard to see," he said. "So when water levels go back up, they say the problem has gone away."

The next step is a cost-benefit analysis of adaptation measures and mitigation strategies in responding to climate-change induced low water levels, Fisher said.

"Climate change is real, it's happening today, the potential economic impact of climate change particularly on water levels is significant," he said. "We need to pay attention because at the end of the day, while the Great Lakes are vast, they are a finite resource."