2019 High Water - Questions and Answers

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January 23, 2020

The following background paper was prepared and reviewed by staff on behalf of the International Joint Commission (IJC) and its International Lake Ontario-St. Lawrence River Board (ILOSLRB).


Over the past several months, the Board has heard from many citizens and communities and seen first- hand the devastating impacts that high water conditions in 2019 have had on shoreline properties and local economies around Lake Ontario, surroundings sectors, and on the upper and lower St. Lawrence River. The Board has taken extraordinary measures to try to alleviate impacts from these exceptional conditions, while considering the consequences for all activity sectors along the Lake Ontario - St. Lawrence River system.

While the conditions of both 2017 and 2019 were exceptional in many ways, similar high water events have occurred throughout the history of Lake Ontario - St. Lawrence River regulation and have the potential to occur again in the future. As such, the purpose of this document is to provide accurate information related to the causes of the high water levels in 2019, as well as actions taken by the Board in attempts to address these conditions through regulation of outflows. The intent is to inform shoreline residents, businesses and communities of the capacity and limitations of outflow regulation to affect conditions so that we can work collectively to identify and assess potential solutions to better prepare for the possibility of extreme conditions and high water events in the future.


Causes of the 2019 High Water Event

This section will answer the following questions:

Question 1. What are the causes of high water levels in 2019?

Question 2. How do high water levels on the other Great Lakes affect Lake Ontario and the St. Lawrence River? 

Question 3. Did the outflow from Lake Erie through the Niagara River set a record in 2019 and how did this contribute to Lake Ontario’s record-high water levels?

Question 4. How much precipitation was received around Lake Ontario and the St. Lawrence River prior to spring 2019, and how does this compare to 2017?

Question 5. Did Lake Ontario total inflows set records in 2019 and how do they compare to 2017?

Question 6. Why did Lake Ontario start rising in November 2018?

Outflows in 2018-19

This section will answer the following questions:

Question 7. Why wasn’t more water released in 2018 when Lake Erie levels were high and downstream flooding wasn’t an issue?

Question 8. Why wasn’t more water released from Lake Ontario during the winter?  Why were outflows reduced during January and February?

Question 9. Why was more water released in January and February 2018 than during the same months in 2019?

Question 10. Why were outflows from Lake Ontario reduced during the spring of 2019?

Question 11. Why were outflows during the spring of 2019 lower than during the springs of 2017 and 2018 and why were they lower for so long?

Question 12. How can outflows impact navigation safety?

Question 13. How effective were the deviation strategies of 2017 and 2019 compared to the strategy employed during the summer of 1993, when outflows were set at alternating rates that temporarily stopped commercial navigation?

Question 14. Why were flows reduced in October for Lake St. Lawrence boat haul-out?

Effects of Regulation

This section will answer the following questions:

Question 15. Would water levels have been lower without the St. Lawrence Seaway and Moses-Saunders Dam?

Question 16. Did Plan 2014 cause the high water levels?

Question 17. Did Plan 2014 hold water back to intentionally raise the level Lake Ontario?

Question 18. Did operation of dams on the Ottawa River system help to reduce flows to the St. Lawrence River?

Question 19. Would the Board have had more flexibility to release water if Plan 1958-D had been in place leading up to the record-high levels of 2019?

Question 20. Why not draw Lake Ontario down each fall so that there is sufficient storage to prevent flooding in the spring?

Potential Future Measures in 2020 and Beyond

This section will answer the following questions:

Question 21. What further actions can be taken to lower water levels and reduce the risk of flooding in 2020?

Question 22. Are these high water levels of 2017 and 2019 the “new normal”?

Question 23. How can shoreline residents and businesses prepare for potential future high-water events?