Why Is The Lake So Cold?

Update: The Lake County Health Department closed Sunrise Beach in Lake Bluff Friday through Monday, Aug. 16, due to a high bacteria count in a test taken on Thursday. Lake Forest's Forest Park Beach is open on Monday and the water is calm...but it is really, really cold at 49 degrees Fahrenheit! 

By Adrienne Fawcett

Lake Michigan has been so cold that even water-loving dogs bolt out after the first exuberant plunge. What's up with these temperatures that are a good 10 to 25 degrees colder than what's considered normal for this time of year?

"We're definitely seeing temperatures that are more typical of early May than of August," said Mike Adam, senior biologist for the Lake County Health Department. "Usually the water starts to slowly warm up in June and July, but this year all of a sudden we had a drop."

A drop is putting it mildly. On August 9, the water temperature at Rosewood Beach in Highland Park was 48 degrees Fahrenheit, and if you've tried to swim in the lake lately, you know that was not a typo. On Sunday, Aug. 16, the water temp at Forest Park Beach was 51 degrees. At this time of year in Lake County, Lake Michigan is usually in the low 70s, said Mr. Adam.

"This happens occasionally," he said of the cold-water trend. "It's a phenomenon that's related to the currents of the lake. If the wind shifts, it may cause some of those currents to 'upwell,' pushing the colder water in toward the shore." The county's Lake Management Unit monitors water temperature, wave height, air temperature and wind direction at its Swim Cast stations in Lake Forest, Highland Park and Waukegan.

Larry McCotter, president of Lake Bluff Open Lands, explained it this way: "Lake temperatures refer to surface water, which is the warmest--as you can experience by diving down just five or six feet. Surface water is blown around by winds, and an offshore wind blows the warmer surface water over to Michigan, which brings the colder water to the surface on our side of the lake." Offshore winds come from the west and southwest.

This explanation is in line with weatherman Tom Skilling's Chicago Tribune column: "Hot weather arrives in the city on brisk south and southwest winds that push the warm surface water out into the lake toward the east shore, allowing the colder bottom water to upwell and replace it."

On the the other side of the lake, swimmers are enjoying much warmer water temperatures. In South Haven, Mich., for example, the water on Sunday was 73.5 degrees F, according to coastwatch.msu.edu.

Mr. Adam said the water will warm up at Lake County beaches, although it's impossible to know when. The water was a mere 51 degrees F at Forest Park on Sunday morning. But last Thursday afternoon, it was in the low 60s in Lake County (prompting a few brave souls to take a dip, as shown in the photo below). The temperature was not of much concern at Lake Bluff's Sunrise Beach, which was closed Friday through Sunday due to high bacteria counts.

We took this photo on Thursday when the water temperature was in the low 60s at Sunrise Beach. A few brave children ran into the lake while others floated on tubes in an attempt to keep all but their back sides dry.

Comments

[lake lover]

Thanks for the explanation- I thought I was just getting old!

[Lise Dominique]

What contributed to the high bacteria levels at the Lake Bluff beach?
How could Lake Forest's beach be open given the proximity of the beaches to each other? That is something that I would like to know more about.

[Mary Cole]

Oh Geez. I swam for an hour on Friday with a group of triathletes, and while it was cold, it was swimable. At least I thought it was until I got the notice later that morning that the beach would be closed for swimming over the weekend due to high bacteria. It came as a surprise, given we'd had no storms prior to Friday. I can only imagine what the bacteria level is today!

[adrienne]

I'm impressed you could swim in the cold water, Mary. How do you do it? If anyone else is training for a triathalon, please offer some advice. I have a wet suit, but it's still too cold for me...Today Lake Forest was 49 degrees!
Adrienne