A map of the three water level and flow control structures in the St. Lawrence River. (Photo: International Lake Ontario – St. Lawrence River Board)
EXPECT HIGHER LAKE ONTARIO OUTFLOWS
May 18, 2017
This week the International Lake Ontario – St. Lawrence River Board assessed current and expected conditions to determine the best outflow release strategy which would continue to address high water level and associated impacts throughout the system. The water level of Lake Ontario is the highest it has been since reliable records began in 1918, breaking the previous record set in June 1952. Lake Ontario is still above the upper regulatory threshold level for this time of year, which allows the Board to continue to maximize the outflows from Lake Ontario to provide all possible relief to riparians living along the shorelines of the entire Lake Ontario – St. Lawrence River system, balancing water levels upstream and downstream to minimize flood and erosion impacts to the extent possible. The Ottawa River flow has been declining rapidly since reaching its record-breaking peak on 8 May. With less flow from the Ottawa River entering Lake St. Louis (near Montreal), higher Lake Ontario outflows in the St. Lawrence River may maintain the high level in Lake St. Louis, which is above its flood level.
Further increases to outflows should be possible in the coming days and weeks. As outflows rise, navigation conditions worsen in the St. Lawrence River from the Thousand Islands to Massena, NY /Cornwall, ON. The Board has notified the St. Lawrence Seaway that these exceptional conditions will likely impact shipping. The Seaway is examining various strategies to ensure the safety of ships transiting this section of the St. Lawrence River.
Following one of the wettest months of April on record, the first week of May 2017 was the wettest recorded since 1900 in terms of total inflows to Lake Ontario from Lake Erie and from widespread, heavy rainfall on the lake and across the Ontario drainage basin. If the drier conditions of the past week continue, outflow is expected to surpass inflow, at which time Lake Ontario’s water level will peak and begin to gradually decline. However, owing to the huge surface area and large volume of water on Lake Ontario, it will take several weeks to significantly reduce levels, and longer to return to more average water level conditions. The Board advises continued caution and preparedness for sustained high water levels in the weeks to come.
On 17 May 2017, Lake Ontario was 75.86 m (248.9 ft), 84 cm (33.1 inches) above its long-term average level for this time of year. The level at Lake St. Lawrence was about 2 cm (0.8 inches) below average, while the level at Lake St. Louis is about 22.51 m (73.8 ft), 97 cm (38.2 inches) above average. At Montreal Harbour, the level is 141 cm (55.5 inches) above average.
The Board continues to monitor the system and will confer again on 22 May 2017. Outflow changes, photos, and graphs are posted to the Board’s Facebook page, and more detailed information is available on its website.
