Extremely high flow conditions are occurring across many areas of the Winnipeg River drainage basin in Ontario, Manitoba and Minnesota following record high precipitation since the start of April and early May. While flows in most natural rivers in the basin are dropping, many remain above previous all-time records. Forecasts indicate that inflows to all major lakes will continue to be exceptionally high, but falling, through the weekend until additional rainfall arrives arrives late Sunday into Monday. The response of rivers to this system will depend on rain, how much falls and where. Water levels will remain high for at least several weeks across most areas of the drainage basin even with dry conditions. Wet weather will prolong the duration of high water levels.
The current level of Lake of the Woods is 323.81 m (1062.4 ft), over 95th percentile level for this time of year. The average lake level rose by 11 cm (4 in) over past week. The lake level has risen above the 2014 peak of 323.78 m (1062.29 ft) and is below the record peak since regulation began of 324.31 m (1064.0 ft), set in July of 1950.
The level of Lake of the Woods is expected to rise by approximately 7-15 cm (3-6 in) over the next 7 days, the rate depending on the rainfall received. Inflow to Lake of the Woods is expected to continue to fall until the rainfall beginning on Sunday, followed by a brief rise, then a return to falling flows. There is the possibility of much higher rainfall over this period, which would cause inflows to rise sharply. Continued rise beyond the 7-day forecast window is expected. The timing of the peak cannot be predicted at this point and will depend on rainfall. Lake of the Woods water levels will likely remain above the Legislated Operating Range for many weeks. Record lake levels are possible and will depend on rainfall across the watershed in the next couple of weeks.
The level of Lake of the Woods is above the top of the Legislated Operating Range, 323.47 m (1061.25 ft). The International Lake of the Woods Control Board has been activated and is working with the Canadian Lake of the Woods Control Board to approve any actions taken with respect to Lake of the Woods. Under Canada-US Treaty, upon reaching a lake level of 323.39 m (1061.0 ft), outflow from the lake must be regulated to avoid exceeding a level of 323.85 m (1062.5 ft). The dams in Kenora have been fully opened since the level of the lake was at an elevation of 323.24 m (1060.5 ft). No additional actions can be taken by the Boards to limit the rate of lake rise, which will depend on rainfall over the coming weeks.
As the lake continues to rise, the level of the Winnipeg River between Kenora and Minaki will also rise. The level rise over the next 7 days below Norman Dam and down to Minaki is expected to be 2-4 cm (1-2 in). This estimate is approximate given uncertainty in the local flows entering the river from tributary areas and the weekend rainfall. The river will continue to gradually rise as long as Lake of the Woods continues to rise and daily fluctuations, up or down, are possible depending on how prevailing winds affect the local level of Lake of the Woods above the dams.
The current level of Lac Seul is 356.54 m (1169.7 ft), over 95th percentile level for this time of year. Lac Seul inflow is extremely high, resulting in a rise of 37 cm (15 in) over the past week. The lake is nearing the Flood Reserve, a range of water levels above the normal operating range defined by federal Order-in-Council that corresponds to a key level for dam safety concern for the Ear Falls dam. To avoid exceeding this range , additional outflow increases took place last weekend, with outflow now at 802 m³/s. This is a very high outflow, last reached in 2008. An additional outflow increase, to 850 m³/s, that was scheduled for Friday, May 27 was canceled. However, depending on the upcoming rainfall, further increases are possible over the next week and will be announced on this Notice Board.
The main body of Lac Seul is expected to rise by 15-25 cm (6-10 in) over the next 7 days. Higher or lower rainfall amounts then currently forecast could see a rise outside of this forecast range.
The flow increases from Lac Seul that took place last weekend will take some time to work down the English River, with an estimate of about two weeks to reach Nutimik Lake.
Manitoba Hydro has provided the following information on the Winnipeg River through the Whiteshell.