2025.09.10 Conditions Update and Lake of the Woods Outflow Reduction
Conditions across the Winnipeg River basin remain dry. High winds over the last week have made it difficult to accurately estimate average lake levels and inflows. The wind is also causing increased water loss through evaporation for the large lakes, and this loss is not being offset by rainfall. Lake of the Woods outflow reductions are therefore needed to slow the lake level decline.
How Wind Affects Water Levels on Large Lakes
We often think of a lake’s surface as flat and still—aside from waves. But on large lakes like Lake of the Woods, wind can cause noticeable changes in water levels from one location to another. This phenomenon is called wind setup. When sustained winds blow across the lake from one direction, they push water toward the far shore, raising the water level there while lowering it on the windward side. This creates a temporary tilt in the water surface. As wind speed, direction, and duration change, so does the distribution of water across the lake.
In early September, strong winds swept across Lake of the Woods, causing noticeable shifts in water levels at different locations around the lake. At first, winds blew from the west, pushing water away from the western shore—where the Cyclone gauge is located—and piling it up along the eastern shore, near the Hanson gauge. Later, as the wind shifted and strengthened from the north, the effects became more visible along the north and south shores. Water levels dropped at gauges on the north shore (Clearwater and Keewatin) and rose at gauges on the south shore (Warroad and Springsteel).
During windy periods, the average lake level computed from the measurements around the lake may change from day to day, even though the amount of water in the lake has changed little. And because lake inflow is computed using the change in lake level over time, this instability also causes inflow values to fluctuate from day to day.
The current level of Lake of the Woods 322.69 m (1058.7 ft) a 15th percentile level for this time of year. The average lake level declined by 3.5 cm (1.4 in) over the past week and is expected to remain stable or decrease by up to 1 cm (0.5 in) over the next week. Lake of the Woods authorized outflow will decrease from 200 to 150 m3/s on Thursday, September 11th.
This outflow change will cause levels along to Winnipeg River to decrease by 8 cm (3 in) below the Norman Dam, by 5 cm (2 in) above Kimberley Rapids and by 2 cm (0.8 in) at the Dalles. This outflow reduction will have no impact on levels at Minaki.
Notice: on Wednesday, September 17th, the Kenora Powerhouse will be shut down for regular station maintenance and Lake of the Woods authorized outflow will be fully transferred to the Norman Dam. Temporary water level fluctuations on the Winnipeg River are expected directly below the dams that day.
The current level of Lac Seul is 356.23 m (1168.7 ft), a 30th percentile level, within the normal range for this time of year. The lake level remained stable over the last week and is expected to increase by 1 to 2 cm (0.5 to 1 in) over the next week. Lac Seul authorized outflow is 125 m3/s with no changes scheduled at this time.