Lake Ontario levels have been dropping rapidly compared to average rates through the months of June and July. The International Lake Ontario-St. Lawrence River Board has been releasing the unprecedented outflow of 10,400 m3/s (367,300 cfs) since June 14 and, despite wet conditions, Lake Ontario levels have fallen 30 cm (12 in.) since peaking in late May.
Lake Ontario levels remain above the IJC's high-level threshold. The board will continue releasing high outflows with the intent to provide all possible relief to Lake Ontario shoreline riparian interests, while balancing the impacts on other affected stakeholders on the St. Lawrence River.
The board met Tuesday to assess current and forecast hydrologic conditions. Total inflows to Lake Ontario have remained very high for this time of year, as have Ottawa River flows into the St. Lawrence River. Levels of Lake St. Louis (near Montreal) set a new record high for the month of July and remain close to record levels for this time of year. Since water levels on Lake St. Lawrence decrease with higher outflow from Lake Ontario, the unprecedented outflow from the Moses-Saunders Dam have resulted in well-below-average levels on Lake St. Lawrence. Furthermore, as water levels on Lake Ontario decline and the outflow remains at 10,400 m /s, velocities in the upper St. Lawrence river will increase resulting in hazardous conditions for shippers and recreational boaters.
Given these conditions, the board discussed current and future outflows from Lake Ontario. The board members understand high water levels and high outflows continue to impact the public and businesses on Lake Ontario and the St. Lawrence River. Currently, the impacts of falling levels and increasing current velocities in Lake St. Lawrence and the St. Lawrence River are increasing as Lake Ontario levels drop. In the interest of providing all possible relief to riparian owners, while balancing the safety risks associated with increased current velocities, outflows from Lake Ontario will need to be gradually reduced in the near future.
The board, in consideration of impacts to public water uses, riparian landowners and businesses, commercial shipping and recreational boating, will maintain the current record outflow of 10,400 m3/s (367,300 cfs) until
Aug. 8, providing conditions remain safe. However, to maintain safe conditions in the system, the outflow is expected to be reduced to 9,910 m3/s (349,970 cfs) on or before that date. This new outflow will be a record high for that time of year to provide all possible relief from high water levels in Lake Ontario, while balancing the impacts downstream.
Water levels are expected to continue to decline rapidly into the fall throughout the system, and outflows from Lake Ontario will remain high. The board, in conjunction with its staff, continues to monitor and reassess conditions on an ongoing basis.
The board specifies the outflows from Lake Ontario according to Plan 2014, as required in the 2016 supplementary order from the International Joint Commission. This plan was agreed to by the U.S. and Canada in December 2016 in an effort to improve environmental performance while maintaining most of the benefits provided to other interests by the previous Plan 1958-D, which was in use since 1963.
In determining outflows, the board, in conjunction with its staff, pays close attention to water levels in the Lake Ontario-St. Lawrence River system and on the Great Lakes upstream, and to the effects on stakeholders within the basin.
Water levels vary from year-to-year and throughout the year depending on weather and water supply conditions. Such variations benefit coastal wetlands and are critical to a healthy lake environment, but may at times and depending on individual circumstances increase the vulnerability of shoreline structures and reduce opportunities for recreational boating activities.
The board urges everyone to be prepared to live within the full range of levels that have occurred in the past and of those that may occur in the future. Based on historical observations and projected future conditions, at a minimum, Lake Ontario water levels are expected to range from a high of 75.73 m (248.5 ft.) to a low of 73.56 m (241.3 ft.) at infrequent intervals.
However, it is also recognized that future climate conditions are uncertain, and more extreme water levels may be reached and these extremes may occur more often.
Levels on the St. Lawrence River tend to vary more widely than on Lake Ontario. Also, these levels do not include the varying local effects of strong winds and wave action that significantly increase or decrease local water levels on both the lake and river, with temporary changes of over half a meter (two feet) possible in some locations.
