Warning for Anglers Fishing in the St. Mary’s River Rapids


The International Lake Superior Board of Control, under authority granted to it by the International Joint Commission (IJC), has set the Lake Superior outflow to 2,400 cubic metres per second (m3/s) (84.8 thousand cubic feet per second (tcfs)) for the month of May, effective May 5th. The outflow of Lake Superior will be adjusted over the next several months to reduce the risk of unusually high flows forecasted for the months of June through August, and to provide more consistent flow conditions in the St. Marys Rapids.

In consideration of the above, the May outflow of 2,400 m3/s (84.8 tcfs) is 150 m3/s (5.3 tcfs) more than that prescribed by Plan 1977-A and is 360 m3/s (12.7 tcfs) more than the April outflow. The May outflow is expected to exceed the capacities of the hydropower plants on the St. Marys River in May, which will be approximately 1,840 m3/s (64.8 tcfs). The excess flow will be released through the control structure at the head of the St. Marys Rapids. As a result, beginning on Monday, May 5th, the gate opening in the control structure will be changed from the present setting equivalent of ½ gate open to four gates fully open. Anglers need to be cautious of the changing flows and water levels in the rapids on May 5th and the unusually high flows and levels that will be experienced in the rapids during May. These gate movements will primarily affect water conditions in the main rapids, but with four gates fully open in the control structure, water may overtop the Fishery Remedial Dike along the north side of the rapids, and may create a hazard. There will be no change to the setting of Gate #1 which supplies water to the channel north of the Fishery Remedial Dike.

The monthly mean water level of Lake Superior in April was 183.27 m. This is 2 cm (1 in) above the long-term (1918-2013) April average and the highest April level since 1998.

This past month the net water supplies to Lake Superior were above average. The level of Lake Superior rose 11 cm (4 in) last month, while on average the lake rises 8 cm (3 in) in April. The Lake Superior level at the beginning-of-May is 4 cm (2 in) above average, and 36 cm (14 in) above the level recorded a year ago at this time. It is 14 cm (6 in) above its chart datum level. The level of Lake Superior is expected to continue its seasonal rise during May.