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Great Lakes water levels in August show uneven trends across Michigan and the basin, with marinas and shoreline towns preparing for late-summer navigation changes.
LANSING, Mich. — The U.S. Army Corps of Engineers reported moderate changes in Great Lakes water levels ahead of August 2025, with Lake Superior rising 5?inches and Lake Michigan?Huron one inch above levels recorded a month earlier. Seasonal declines are projected for most lakes, raising concerns for Great Lakes and Michigan shoreline users.
Forecasted Great Lakes water levels show small gains but risks loom for Michigan marinas
The forecast outlines a modest one?inch increase in Lake Michigan?Huron by Sept.?1, while Lakes St.?Clair, Erie and Ontario may decline by 3 to 4?inches. Lake Superior is expected to rise another inch.
Despite being 1?inch above July 1 levels, Lake Michigan?Huron remains 9?inches below levels from Aug.?1,?2024, and 4?inches below lthe ong?term August average. The rise in Lake Superior offsets a zero?change relative to last year, but the lake is still 2?inches below its long?term August average.
Weather patterns across the basin shaping Great Lakes water levels
The Great Lakes basin saw much hotter weather than usual last week, with air temperatures up to 10?°F above average in parts of Michigan such as Iron Mountain, where highs approached the 90s. Most of the basin saw near?normal precipitation; however, southeast Michigan received nearly 4?inches over several days, boosting runoff.
Michigan shoreline users urged cautious planning amid channel and outflow shifts
Lake Michigan?Huron’s outflow via the St.?Clair River is projected to be below average in August, while outflows from Lake St.?Clair into the Detroit River and from Lake Erie through the Niagara River are expected to be above average (lre-wm.usace.army.mil). That may affect navigation depth around ports, including Sarnia?Port Huron and Detroit.
Boaters, dock operators, and marina managers in the Michigan Thumb region should review up?to?date local Great Lakes water levels before planning launches or maintenance, the Corps notes (ijc.org).
Expert insight: Great Lakes water levels follow expected seasonal decline
University of Michigan hydrologist Dr. Drew Gronewold highlighted the evolving volatility in Great Lakes water budgets, noting that:
“Over the past two decades, water levels on the Great Lakes have gone through an unprecedented period of persistent below?average conditions, a record?setting rate of water level rise and, now, a series of record?setting high levels.”
He explained that these shifts stem from “unusual combinations of extreme lake evaporation, persistent increases in the magnitude and intensity of precipitation events, and intermittent outbursts of cold arctic air.” He emphasized that these changing hydrologic conditions “warrant careful consideration of planning decisions related to coastal and water management infrastructure, zoning ordinances, and other considerations related to human health and safety.”
Michigan implications: marinas, infrastructure and shoreline economy remain vulnerable
Many Michigan marinas depend on predictable depth for slip access. Even slight declines—3 to 4?inches—can reduce navigable depths in harbors built to minimums. The Thumb region’s shoreline town economies rely on tourism and boating through late summer. Adjustments to dock operations and dredging schedules may be required.
Meanwhile, Lake Superior’s modest rise may benefit northern Michigan ports lightly, though its levels still sit below long?term averages. Lake Erie and Ontario show modest deficits, too, though Lake St.?Clair currently sits 4?inches above average, helping maintain depth in connecting waterways.
Great Lakes water levels well below record highs but above historic lows
All five Great Lakes remain well below record high monthly average levels for August—Lake Michigan?Huron is still 37?inches below its record high mean of 2020. Conversely all remain well above their lowest historic August mean levels, offering some relief (lre-wm.usace.army.mil).
Related Great Lakes Water Level News
- Ottawa County, Michigan, is facing groundwater shortages despite proximity to Lake Michigan—a possible concern if lake?basin supply remains low (glc.org).
- The Army Corps is also starting maintenance dredging at Manistique Harbor, U.P., as soon as Aug.?7, which may be coordinated with Great Lakes water levels shifts (glc.org).
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