Forget the ocean. Lake Michigan just served up the kind of surf report you’d expect from a major swell event in the Pacific.

A powerful October storm turned the freshwater lake into chaos, blasting lighthouses and shorelines with enormous waves. Footage circulating on Instagram and YouTube shows the extraordinary spectacle.

And those reports of 20-foot waves? They’re not just social-media hype.

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In its October 16 forecast , the National Weather Service predicted waves of 15 to 20 feet across southern Lake Michigan, with occasional individual waves reaching 26 feet.

Northerly winds were forecast to reach 45 knots—roughly 52 mph—as low pressure moved east of the Great Lakes and strong high pressure built to the west.

There’s an important distinction: these were forecast heights, not independently verified measurements.…