Record high water levels on the Great Lakes could cost $1 billion, a shipping industry group warned this week.

The water level on Lake Ontario sat at 75.91 meters Tuesday, well above June’s long-term average of 75.05 meters, causing flooding along its shoreline.

To alleviate flooding, the Moses-Saunders Dam, downriver from Lake Ontario on the Saint Lawrence River, has upped its flow rate to 10,400 cubic meters per second and will consider increasing that flow rate again Friday.

That’s causing controversy among landowners along the shoreline who want higher flow rates so lake levels lower quicker. The shipping industry, which uses the St. Lawrence Seaway to connect the Great Lakes to the Atlantic Ocean, says increasing flow rates beyond 10,400 cubic meters per second would cause major delays and be too costly.

In a news release this week, the Chamber of Marine Commerce urged the International Lake Ontario-St. Lawrence River Board, an arm of the International Joint Commission that manages levels along waters shared by Canada and the United States, not to push flow rates beyond current rates because it would cost $760 million and $1.3 billion in business revenue losses in Canada and the U.S.

Anything higher would prevent ships from safely anchoring and could cause navigation buoys to drift away, the Chamber said.

The Board is considering raising the flow rate in intervals, allowing shipping to take place on days with current flow rates then halting shipping when flow rates increase. Another option includes stopping shipping on the seaway for several weeks this season to maintain a higher flow rate until water levels fall.

The Duluth Seaway Port Authority is urging the Board to keep its flow rates at the level it set last week.

“To us, that’s reasonable. That makes sense,” Executive Director Deb DeLuca said of current rates. “It’s slowing shipping as it is. Under the current scenario, shipping is delayed and slowed and there is an economic impact to that, but we’re OK with that.”

DeLuca didn’t have estimates on what the impact would be for the Port of Duluth-Superior, but noted the port has already seen, and expects to see more, international shipments of windmill components, grain and iron ore coming and going from the port.

In 2018, the Port of Duluth-Superior saw the arrival of 66 overseas ships, or salties, that passed through the Saint Lawrence Seaway.

The Board hadn’t made a decision before Friday’s meeting, but was listening to all stakeholders.

“Even with high outflows, it is expected that Lake Ontario will remain stable or decline slowly for the next several weeks,” the Board said in a release Monday. “The Board continues to seek any opportunity to lower Lake Ontario faster than what is presently possible, and will be meeting again this week to review its regulation strategy.”