Image of St. Marys River Control Structures

Update on Lake Superior Outflows and Expected Conditions - April 2021


While Lake Superior and Lake Michigan-Huron water levels remain above average, the risk of high-water impacts remains.  Lake Superior outflows continue to be set in consideration of high levels upstream and downstream.

Last month, Lake Superior declined 2 cm (0.8 in), while on average it declines 1 cm (0.4 in) in March. Lake Michigan-Huron remained stable over the course of the month, while on average it rises 5 cm (2 in) in March.  

Both lakes appear to be near their seasonal low points and are expected to begin their seasonal rises. There  continues to be an increased risk of shoreline erosion, lakeshore flooding and coastal damages. The International Lake Superior Board of Control (Board) advises all those that may be affected to prepare for potentially severe coastal impacts, especially during periods of strong winds and high waves.

ILSBC April 2021 Infographic

At the beginning of April, Lake Superior is 18 cm (7.1 in) above average (1918 – 2020), 18 cm (7.1 in) below its level of a year ago, and 20 cm (7.9 in) below its record-high level of 1986. Lake Michigan-Huron is 62 cm (24.4 in) above average and 32 cm (12.6 in) below the record-high level at this time last year.

The Board expects the total outflow to be 2,010 m3/s (71 tcfs) in April, which is as prescribed by Lake Superior Regulation Plan 2012. The gate setting of the control structure will be maintained at the setting equivalent to one-half gate open in April.

Shoreline businesses and property owners are reminded that the Great Lakes – St. Lawrence River Adaptive Management (GLAM) Committee continues to host an online questionnaire to allow for direct reporting on impacts related to recent high water conditions: