GRAND HAVEN, Mich. (Michigan News Source) – Multiple waterspouts have been spotted swirling over Lake Michigan this week, prompting one surprised observer to say: “I think that’s a water tornado!”

Patrick Beilfus, who happened to be visiting from Chicago, told Fox 6 that he couldn’t believe his eyes.

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“I didn’t think it was real,” he said. “I have this old memory of that movie Twisters or something.”

Beilfus was right about one thing—these enormous columns of wind and water can be similar to offshore tornadoes. They may form during thunderstorms, in which case they’re called tornadic waterspouts, or they can be “fair weather waterspouts” that form during relatively calm weather. The latter are typically less dangerous and slow-moving.

Waterspouts are most common in the Florida Keys and the Gulf of Mexico, according to EarthSky. They also frequently occur in the Great Lakes around the end of summer, as cold air from the north passes over the relatively warm lake water. This temperature differential may produce swirling winds, which can suck up water from the surface and form a towering funnel of water.

Earlier this week, the International Centre for Waterspout Research reported 30 confirmed waterspouts over Lakes Ontario, Erie, Huron, and Georgian Bay. More waterspouts are expected to form this morning.

According to the National Weather Service, boaters who live along the Great Lakes should be aware of the hazards posed by waterspouts, which can be almost as dangerous as tornadoes. Those who identify a waterspout should move at a 90 degree angle from the spout’s apparent motion, without attempting to navigate through it.