Weekly Regulation Summary

Summary for Week Ending 3 March 2021

As of 1 March 2021, Lake Ontario outflows are as prescribed by Plan 2014. The average Lake Ontario outflow is expected to be 8080 m³/s for the coming week, which is the amount specified by the regulation plan. For more information, see the Board's latest news release: https://ijc.org/en/loslrb/lake-ontario-and-upper-st-lawrence-river-flood-risk-diminishes-very-high-outflows-continue

  Week Ending: Wed, 03 Mar 2021 Average this time of the year (c) 
Lake Ontario -    
         Actual end of week level: 74.49 m  (244.39 ft) 74.64 m  (244.88 ft)
         Computed Plan 2014 Level (a): 74.58 m  (244.69 ft)  
         Computed Preproject Level (b): 75.47 m  (247.60 ft)  
         Weekly Mean Outflow: 8400 m³/s  (296600 ft³/s) 7210 m³/s  (254600 ft³/s)
         Weekly Total Supply: 7830 m³/s  (276500 ft³/s) 7610 m³/s  (268700 ft³/s)
Lake St. Lawrence at Long Sault Dam Weekly Mean Level:  72.16 m  (236.75 ft) 72.53 m  (237.96 ft)
Lake St. Louis at Pointe-Claire Weekly Mean Level:  21.58 m  (70.80 ft) 21.38 m  (70.14 ft)
Montreal Harbour at Jetty #1 Weekly Mean Level:  6.82 m  (22.38 ft) 6.97 m  (22.87 ft)
Ottawa River at Carillon Weekly Mean Outflow: 2170 m³/s  (76600 ft³/s) 1940 m³/s  (68500 ft³/s)
Preliminary Lake Ontario Outflow for Week Ending Fri, 12 Mar 2021: 8080 m³/s  (285300 ft³/s) 7350 m³/s  (259600 ft³/s)

Levels are in metres (feet) IGLD 1985.  Supply and flows are in cubic metres (feet) per second m³/s (ft³/s).  

(a) Levels that would have occurred with strict adherence to Plan 2014.

(b) Levels that would have occurred had there been no Lake Ontario regulation.        
(c) For comparison purposes, Lake Ontario water level data since 1918 are used to be consistent with those published in the  US and Canadian Great Lakes bulletins (https://www.waterlevels.gc.ca/C&A/bulletin-eng.html). Other averages are for the periods as follows: Lake Ontario outflows and levels at Long Sault and Pointe-Claire since 1960; Montreal since 1967; and Ottawa River outflow at Carillon since 1963.

The regulation plan for Lake Ontario specifies a weekly average outflow from Saturday through the following Friday, inclusive.  To provide timely information for the coming week to the hydropower and Seaway operators, and our readers, we complete the regulation plan calculations each Thursday.  Our calculations use the data available at the time, which are from the previous seven days (Thursday through Wednesday). Since the two time periods do not exactly coincide, their data are usually slightly different.

The table shows the actual flow for the week ending Wednesday.  It also gives the preliminary flow for the coming week ending Friday.  We emphasize that this is the preliminary flow, since unforeseen flow changes may occur after we have issued our notice.  When these flow changes occur, they are reflected in the subsequent week's notice.

Information in this report is compiled from provisional data provided by: Environment & Climate Change Canada, Fisheries and Oceans Canada, Hydro Quebec, Ontario Power Generation Inc, the New York Power Authority, and the U.S. National Ocean and Atmospheric Administration.