Weekly Regulation Summary
Summary for Week Ending April 23, 2025
| Week Ending: Wed, Apr 23 2025 | Average this time of the year (c) | |
| Lake Ontario - | ||
| Actual end of week level: | 74.84 m (245.54 ft) | 74.95 m (245.90 ft) |
| Computed Plan 2014 Level (a): | 74.84 m (245.54 ft) | |
| Computed Preproject Level (b): | 75.18 m (246.65 ft) | |
| Weekly Mean Outflow: | 7210 m³/s (254600 cfs) | 7220 m³/s (255000 cfs) |
| Weekly Total Supply: | 8490 m³/s (299800 cfs) | 8580 m³/s (303000 cfs) |
| Lake St. Lawrence at Long Sault Dam Weekly Mean Level: | 73.50 m (241.14 ft) | 73.55 m (241.31 ft) |
| Lake St. Louis at Pointe-Claire Weekly Mean Level: | 21.58 m (70.80 ft) | 21.75 m (71.36 ft) |
| Montreal Harbour at Jetty #1 Weekly Mean Level: | 6.95 m (22.80 ft) | 7.53 m (24.70 ft) |
| Ottawa River at Carillon Weekly Mean Outflow: | 4060 m³/s (143400 cfs) | 3750 m³/s (132400 cfs) |
| Preliminary Lake Ontario Outflow for Week Ending Fri, May 02 2025: | 7260 m³/s (256400 cfs) | 7340 m³/s (259200 cfs) |
Levels are in metres (feet) IGLD 1985. Supply and flows are in cubic metres (feet) per second.
(a) Level that would have occurred with strict adherence to Plan 2014.
(b) Level that would have occurred had the hydropower project, associated dredging and subsequent outflow management not been undertaken.
(c) Historical statistics are based on the available period of record for each dataset: Lake Ontario Water Levels (1918-2022); Lake Ontario Outflows (1900-2022); Net Total Supplies (Inflows) (1900-2022); Lake St. Lawrence Water Levels (1960-2022); Lake St. Louis Water Levels (1960-2022); Montreal Harbour Water Levels (1967-2022); Ottawa River Outflows (1963-2022).
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.