Update on Upcoming Outflows and Expected Conditions

The Board expects the total St. Marys River flow in April to be 1,790 m³/s (63,200 ft³/s) as prescribed by Regulation Plan 2012.

The gate setting of the Compensating Works at the head of the St. Marys Rapids will remain at the typical winter gate setting of one-half gate open (Gates #1 and #7 through #10 open 20 cm (8 in) each). The St. Marys Rapids flow will remain at approximately 84 m³/s or 3,000 ft³/s. The Poe Lock reopened March 25, 2026.

Water level changes over the month of March

Water supply conditions were near average in the Lake Superior basin while conditions were much wetter than average in the Lake Michigan-Huron basin in March.

• Lake Superior decreased by 2 cm (0.8 in) last month which is in accordance with the seasonal long-term average pattern for Lake Superior to decline by 2 cm (0.8 in) in March.
• Lake Michigan-Huron increased by 15 cm (5.9 in) last month while the seasonal long-term average pattern is for Lake Michigan-Huron to increase by 5 cm (2.0 in) in March.

Water levels as of the beginning of April

• At the beginning of April, the estimated lake-wide average water level of Lake Superior was 9 cm (3.5 in) below the seasonal long-term average (1918-2024) and 6 cm (2.4 in) above the level of a year ago.
• At the beginning of April, the estimated lake-wide average water level of Lake Michigan-Huron was 19 cm (7.5 in) below the seasonal long-term average (1918-2024) and 6 cm (2.4 in) below the level of a year ago.

Forecast outlook in April

• If weather and water supply conditions are near average, Lake Superior may rise by approximately 7 cm (2.8 in) and Lake Michigan-Huron may increase by approximately 10 cm (4.0 in).
• If conditions are much wetter than average, Lake Superior may increase by approximately 16 cm (6.3 in) and Lake Michigan-Huron may rise by approximately 19 cm (7.5 in).
• If conditions are much drier than average, the water level of Lake Superior may increase by 1 cm (0.4 in), and Lake Michigan-Huron may increase by about 3 cm (1.2 in).

The International Lake Superior Board of Control is responsible for managing the control works on the St. Marys River and regulating the outflow from Lake Superior into Lake Michigan-Huron. Under any outflow regulation plan, the ability to regulate the flow through the St. Marys River does not mean that full control of the water levels of Lake Superior and Lake Michigan-Huron is possible. This is because the major factors affecting water supply to the Great Lakes (i.e. precipitation, evaporation, and runoff) cannot be controlled and are difficult to accurately predict. Outflow management cannot eliminate the risk of extreme water levels occurring during periods of severe weather and water supply conditions. Actual flows will vary hour-to-hour and day-to-day depending on hydrologic conditions and variations in flow at the hydropower facilities. Additional information can be found on the Board's homepage: https://ijc.org/en/lsbc.