Lake Ontario lower than in 2017 despite temporary outflow reductions

Water levels across the Lake Ontario-St. Lawrence River system have begun their typical spring rise, but several months of high outflows combined with favorable winter weather conditions has levels back within their normal range and well below those seen during the historic high water event that began about a year ago. Outflows from Lake Ontario continue to be set according to Plan 2014 and, even with recent reductions necessary to ensure safe navigation and to reduce flood risks in the St. Lawrence River, they remain above average in response to above-average levels of both Lake Ontario and the upper Great Lakes.

As is typical in spring, outflows from the Ottawa River into the St. Lawrence River have risen significantly in response to increased snowmelt and springtime precipitation. However, the Ottawa River Regulation and Planning Board recently noted that Ottawa River outflows are expected to remain within the normal range of fluctuations for this time of year. Accordingly, the International Lake Ontario-St. Lawrence River Board has temporarily reduced outflows from Lake Ontario to balance the risks and impacts of upstream flooding and erosion (on both Lake Ontario and in the Thousand Islands), with the risks of similar impacts downstream in the St. Lawrence River from Montreal through to Three Rivers.

At this time, the risk of significant flooding either upstream or downstream remains low. There are currently no indications that the extreme rainfall that resulted in record Lake Ontario flooding and Ottawa River flows, and flooding along many areas of the lower St. Lawrence River in 2017, will occur again this year. Flow reductions from Lake Ontario are expected to be temporary and as the Ottawa River and levels downstream on the St. Lawrence begin to subside, outflows from Lake Ontario can be increased again.

The board, in conjunction with its staff, continues to monitor conditions. Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available here.

Maritime Editorial