After a winter of next-to-no snow, water levels all across the Great Lakes are down this spring, something government and business experts say could have an impact on the environment and the economy.

The Canadian Hydrographic Service issued a warning earlier this month that water levels were at potentially dangerous levels on the lakes system, which stretches from Lake Superior in northwestern Ontario to Montreal.

The water is running so low that boaters risk running aground on rocks that would usually be well under water, the service said.

"Mariners should exercise extreme caution throughout the entire system, especially during periods of strong winds when water levels can rise or fall significantly in a short period of time."

Water levels in Lake Superior, the largest of the lakes, are at their lowest in more than a century, according to officials on both sides of the Canada-U.S. border.

The U.S. Army Corps of Engineers reported this month that in April, the biggest of the Great Lakes lost about three centimetres during a time when spring runoff usually swells the lake by as much as eight centimetres.

The Corps said that was only the fourth time Lake Superior declined in April in the past 110 years and was the lowest level since 1907. The levels are also low in lakes Huron, Michigan, Erie and Ontario -- as much as 25 centimetres lower in some places.

But levels are at their lowest along the St. Lawrence River, falling to more than 50 centimetres below the average for this time of year.

The International St. Lawrence River Board of Control said this week that it will take several days of soaking rain to restore water levels to normal and warned that the low water could cause problems for boaters, fishermen and the tourism industry.

Maurice Noel has cast his line into the river near Montreal for decades but said that this season the fish aren't biting.

"You can't catch any fish," Noel told CTV Montreal. "I've never seen the water so low in my life."

Ferry operator Gary Cote said he too has never seen the river running so low.

"Usually at this time it's up to about here, it's gone down," Cote said.

That has led to wetlands drying up, fish not spawning and increasing water pollution. It has also led to dwindling drinking water supplies in some towns along the St. Lawrence.

Managers of the St. Lawrence Seaway have said they are monitoring the water levels closely because vessels have to lighten their loads along the busy shipping corridor to make it through shallower channels.

Those who manage the water levels can usually open a dam upstream to raise water levels, but this year the levels upstream are too low to allow that.

And there is no prospect for improvement this summer. The long-term forecast for the region calls for drier than normal conditions.