The hot, dry spring across much of Ontario and Quebec has resulted in low water levels in most lakes and rivers, prompting shipping restrictions for freighters and warnings for pleasure boaters.

The shipping season in the Great Lakes has been open for less than two months and commercial freighters are being told to lighten their loads because of low water levels.

Commercial freighters that haul coal, cement and aggregates across the lakes and along the St. Lawrence are adapting to the change, said Angus Armstrong, harbourmaster for the Port of Toronto.

"There will be some impact on cost. They might come in with 30 to 40 tonnes less to ensure they come in with enough water," he told CBC News.

Downstream near Montreal, the water level is close to 1.5 metres below last year.

"If you just look out in the lake you can see rocks out over there and normally you don't see any of that," said Doug Sladen who sails with the Il Perrot Yacht Club.

Fellow sailor Claude LaFontaine said the water levels are the lowest he has seen in 30 years.

"We had a couple of boats hit bottom and some had problems getting out of the harbour."

Back in Toronto, Armstrong said the key to navigating with lower water levels is caution.

"Take your time, go slow, because what used to be a passable little canal in 2008, 2009, may not be passable now."

The conditions are likely to continue as Environment Canada predicts a hot and dry summer throughout the region.