Weekly Regulation Summary

Summary for Week Ending 25 March 2020

Lake Ontario outflows continue to be maximized to the extent possible, with adjustments made as necessary depending on water levels in the Montreal area, which remain near record-highs owing to near record-high Lake Ontario outflows and above-average Ottawa River flows. Widespread rainfall and mild temperatures are forecast for this weekend and Ottawa River flows are expected to rise. The St. Lawrence Seaway is also scheduled to open 1 April. Outflows will be adjusted as necessary.

  Week Ending: Wed, 25 Mar 2020  Average this time of the year (c) 
Lake Ontario -    
         Actual end of week level: 75.21 m  (246.75 ft) 74.72 m  (245.14 ft)
         Computed Plan 2014 Level (a): 75.34 m  (247.18 ft)  
         Computed Preproject Level (b): 76.11 m  (249.70 ft)  
         Weekly Mean Outflow: 9690 m³/s  (342200 ft³/s) 7350 m³/s  (259600 ft³/s)
         Weekly Total Supply:                     9980 m³/s  (352400 ft³/s) 8300 m³/s  (293100 ft³/s)
Lake St. Lawrence at Long Sault Dam Weekly Mean Level:  72.81 m  (238.88 ft) 72.92 m  (239.24 ft)
Lake St. Louis at Pointe-Claire Weekly Mean Level:  22.24 m  (72.97 ft) 21.36 m  (70.08 ft)
Montreal Harbour at Jetty #1 Weekly Mean Level:  7.74 m  (25.39 ft) 6.92 m  (22.70 ft)
Ottawa River at Carillon Weekly Mean Outflow: 3280 m³/s  (115800 ft³/s) 2150 m³/s  (75900 ft³/s)
Preliminary Lake Ontario Outflow for Week Ending Fri, 03 Apr 2020: 10200 m³/s  (360200 ft³/s) 7340 m³/s  (259200 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.