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Iroquois Dam. Photo courtesy New York Power Authority
Iroquois Dam. Photo courtesy New York Power Authority

Why low Lake Ontario levels mean high St. Lawrence levels

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We've reported for months - years even - that the Great Lakes, from Superior to Ontario, are at historically low water levels.

So we were surprised to get the news this week that regulators are lowering the gates at the Iroquois Dam near Ogdensburg because the St. Lawrence River is too high.

It's quite a puzzle.

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Last weekend, shoreline homeowners and boaters between Ogdensburg and Massena were alarmed to look out the window and watch the St. Lawrence rise.

Dalton Foster is president of the Wilson Hill Association and an expert on water levels in this part of the St. Lawrence. He said the shore was "eroding away. A lot of people had their boats damaged. Docks were under water."

Here's why this happened: Regulators are trying to do something about those low water levels on Lake Ontario. So they're letting less water through the hydropower dam near Massena. In other words, they're trying to hold back water and store it on Lake Ontario.

The problem was, says Foster, west and southwest winds whipped up at the same time, basically pushing water across Lake Ontario and into the St. Lawrence.

That pushes more water down the river, Foster says, and because regulators were still letting less water go through the dam in Massena, the river had nowhere to go but up; hence the flooding.

So Wednesday, regulators decided to try something else. They lowered the gates of the Iroquois Dam, a much smaller structure upriver from the big Massena power dam.

John Kangas, U.S secretary of the International St. Lawrence River Board of Control, says the gates of the Iroquois Dam are normally raised and kept above the water level, "to allow recreational boats to go back and forth."

How does this work? Picture a bunch of garage doors above the river. Wednesday, Kangas ordered those garage doors to be dipped down into the water. And that restricts the water flow and lowers the river several inches.

"This doesn't hold back the water. The same amount of water is going through the river. What it does is just change the river profile a little bit."

The Wilson Hill Association's Dalton Foster says lowering the gates at Iroquois Dam has helped lower the River's level…a little. "Yesterday it was down, but now it's coming back up again, because the wind has shifted again."

So we have two takeaways. Regulator John Kangas fears more dry weather this summer, so he's trying to store two inches of extra water on Lake Ontario to release this fall, to help with drinking water intakes and boating.

"Fall tends to be a kind of critical time. St. Lawrence is falling. Lake Ontario is falling. Ottawa River is normally falling. There might be a need to put a little bit more water down the St. Lawrence River to help out the downstream with their intakes and navigation."

The second takeaway, says Dalton Foster, is that one man-made change to this vast natural system has many consequences. "It will have many effects and it will have different effects all the way down the river."

That means if you live along the river from Ogdensburg to Massena, look out for your docks and boats.

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