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Lake Michigan's waves Tuesday didn't just stir up swift currents, colder water temperatures deeper in the lake were forced to the surface.

(MLive.com File Photo)

Lake Michigan temperatures in the upper 70s last week since have crashed almost 20 degrees.

HOLLAND, MI — The days of comparing Lake Michigan's water temperatures to bath water are no more: A roller coaster sounds much more accurate.

Water temperatures began their tumble Tuesday afternoon, with Saugatuck's Oval Beach reporting an 8-degree drop earlier Wednesday morning, according to National Weather Service data.

An even more impressive reading was reported just northwest of Holland. A nearshore buoy recorded a water temperature of around 80 degrees yesterday to a biting 56 degrees this morning.

Strong winds created dangerous wave action along the West Michigan shoreline as a cold front moved through Tuesday and pushed water toward the coastline. At the same time, water near the shore was forced away.

This created a process known as upwelling, where colder water in the deeper parts of the lake rose to the surface, according to the National Weather Service in Grand Rapids.

Last week's heat wave warmed the lake and held temperatures at above normal levels. If the weekend forecast is any indication, those conditions shouldn't be expected to return anytime soon.

Andrew Krietz can be reached through email and Twitter.