Lake St. Lawrence not likely to burst banks, official confirms

Lake St. Lawrence. Nation Valley News file photo

Lake St. Lawrence is perpetually flooded and controlled by dams

MORRISBURG — While theoretically possible, Lake St. Lawrence — an already perpetually-flooded body of water fronting municipalities between Cornwall and Iroquois — is unlikely to ever burst the banks created by the 1950s Seaway project, says the Canadian Regulation Representative on the International Lake Ontario – St. Lawrence River Board

To the contrary, residents of South Dundas and South Stormont should expect to see their artificial lake drop by a meter or more in days to come as higher volumes discharge through at the Moses-Saunders Dam in Cornwall.

That’s according to Rob Caldwell in an emailed Q&A with Nation Valley News.

The lake, part of the St. Lawrence River and still more commonly known by that name, is not currently at a record high level, according to Caldwell. However, points west of Iroquois Dam, beyond the lake, do find themselves at an historical high point.  And Caldwell clarified that levels there are indeed likely to go up by “several centimetres” before higher flows through the Cornwall Dam make an impact.

South Nation Conservation has issued a flood watch for the river in general, affecting Augusta Township to South Dundas. The watch does not differentiate between Lake St. Lawrence and the rest of the river.

Q. … when flows are increased through the Cornwall dam, doesn’t that really drop the level of Lake St. Lawrence from Iroquois to Cornwall?  

A. Yes, correct.

Q. How much is Lake St. Lawrence likely to drop in places like Morrisburg over the next few days as flows increase through the dam? Will it be a marked decrease very obvious to residents and boaters? 

A. Likely will get quite low, possibly dropping by over a metre eventually. Yes it will be very obvious.

Q. Also, in a … press release today, you are quoted as saying the river may rise “a bit” before that drop starts to happen. Does “a bit” mean an inch or a foot?

A. That depends on water supplies and winds, but yes, I meant likely several centimetres. 

Q. Is the river at an historical high right now … ? 

A. Yes, above [west of] Iroquois. 

Q. If it goes up a bit more yet, could we hit a new record for water height on Lake St. Lawrence?

A. No, since we control the levels on Lake St. Lawrence by partially lowering gates at Iroquois Dam.

Q. Since the river [Lake St. Lawrence] has been in a state of constant “flood” since 1958 … is there really any threat of its “new” banks ever being seriously breached in places like Morrisburg, Iroquois, and Long Sault? (The water is always artificially high there.)

A. Theoretically, yes, if Lake Ontario rose high enough and we had to reduce flows low enough for some reason. At the extreme, if there was no flow somehow at Moses-Saunders, the level would be the same as on Lake Ontario. But in all but such hypothetical cases, very likely not.

Q. Also, is New York getting its wish, in that an attempt is being made to release more water out of Lake Ontario?

A. No, the board, on its website, issued a press release explaining that we will continue to maximize the outflows from Lake Ontario while minimizing and balancing flood and erosion impacts upstream (Lake Ontario and 1000 Islands) and downstream (from Lake St. Louis to Lake St. Peter) by maintaining a certain threshold level on Lake St. Louis. Now that the Ottawa River inflows to the St. Lawrence have peaked today, we can start increasing Lake Ontario outflows. We made an increase at midnight last night, and should be able to further increase them as early as tomorrow around noon.


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