How Lake Michigan's Thermocline Works

Mornin' to everyone counting down the days till a Packers kickoff. This is the Wiscampsin Weekly - the email that gets you in the know on the Wisconsin outdoors in 5 minutes or less. New reader? Subscribe here.

This week's bone chilling email:

• Lake Michigan's icy water works 🧊 

• The elusive 40 lb. King salmon 🐠 

• State Parks and Forests sticker contest winner (it's pretty neat) 🌲 

Swimming in Lake Michigan's Thermocline

When we started diving into the unique, strangely technical aspects of Lake Michigan's water mechanics (and why it's so darn cold even in the summer), we thought we'd get some outside opinions from folks around the state. After all, 'cold' can be a pretty subjective word, especially here in Wisconsin.

Here's what a few folks said:

"Swimming in the lake? Criminy cripes there guy, gonna be an ice cube when you're done! Reminds me, need some more ice for my Old Fashioned..."

"Cold? That's not cold. I was at the 1967 Ice Bowl at Lambeau Field there, sonny. My coon skin cap kept me plenty warm, but a few of my toes didn't make it."

"Why swim in the lake when you can drink beer next to the lake?"

...Alright, so it's a mixed bag on how cold it really is. But regardless, anyone who takes a dive into Lake Michigan knows that while the surface may be "warm" (hovering around 70 degrees in Milwaukee in late summer), it can be frigidly cold just a few feet below the surface.

Lake Michigan's Water

• Deepest depth of 922 feet, with an average depth of 279 feet

• "Turns over" twice a year due to varying temperatures and water density

• In the summer, forms a thermocline, or gradient of harshly varied temps at different depths

The changing of the seasons

We've all been there - you dip a toe in, think hey, the waters fine, only to dive in and find it's colder than your high school boyfriend's heart after graduation. Damn you, Keith!

It's all because of the thermocline.

You see, water temperature is affected by daily and seasonal weather conditions (like wind, sun, cloud cover, etc.), which creates some pretty interesting outcomes through the year.

Winter

Colder temps causes the surface water to cool, eventually bringing the entire water column (from the surface to bottom) to near-freezing temps.

Spring

As the sun finally starts to show itself, the lake's surface begins to warm. When this surface water reaches exactly 39.2 F, it becomes heavy and sinks.

The high winds also help, acting like a stirring stick to mix the waters. Eventually, the water at the surface will sink to the bottom, and the lake will have "turned over." This happens once in the spring and again in the fall, making Lake Michigan a dimictic lake.

Summer

As the winds die down, the lake isn't mixed as easily, and soon the surface water is warmed by the sun, while the bottom remains very cold. In between, you'll find a barrier called the Thermocline, a gradient of different water temps at different depths.

Fall

As the summer days come to an end, the surface water begins to cool. When that surface water reaches that magical 39.2 F, it reaches its maximum density and sinks. Alas, the lake turns over once again.

What goes around comes around

This mixing or "turning over" of the Lake's water is actually pretty crucial.

With each turning over, the lake circulates nutrients, dispersing them throughout for all the lake critters to enjoy.

As the zooplankton feed on the little stuff, everything further up the food chain benefits.

That's why the Thermocline is so great for salmon fishing. There's better oxygen and better bait for the fish to munch on in the colder waters.

But unfortunately, water temps are progressively warming each and every year.

Originally dismissed because only the surface water temps were rising, deep-water thermometers are showing that even the very bottom of the lake is being affected too.

Why does it matter? If the bottom layer of water becomes too warm, the lake will only turn over once a year (instead of two), greatly affecting that nutrient dispersal described above.

Which means... potentially less baitfish, less big fish, and less fish fry's for you and me.

But the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory says with enough effort, the warming waters can be reversed.

So that's where we come in. Share this email with a friend, read more about conserving Lake Michigan's thermocline, and geek out on these groovy graphs.

But most importantly...

Get out 'der!

The "Holy Cripes" Moment of the Week❗️

No better way to get amped for your Wednesday than watching Bald Eagles in central Wisconsin to EDM music at 6 a.m. AMERICA!

Nuts and Seeds 🌰 

🎣 That's a keeper!: A 'Scon fisherman landed a 40.4 lb Chinook (King) salmon, surpassing the elusive 40 lb mark that hasn't been crossed in nearly 30 years. The state record, a 44.9 pounder, was hauled in in 1994 in Sturgeon Bay. Make room in da freezer, Sheryl!

🌲 Winner winner, fish fry dinner: Brookfield East High School senior Brooke Salomone won the 2022 State Parks and Forests Vehicle Admission Sticker Contest with her stellar sticker design. After a couple Spotted Cows, we may even get this thing inked on us, it's that neat...

🦌 Citizen Science Survey: The DNR is asking for the good folks of Wisconsin to help them out with this survey on deer and game birds. By comparing the fawn/doe and poult/hen ratios from years' past, they can manage the population better. Just in time for huntin' season.

An (Admittedly) PG-13 Review From the Trail

*To whoever left this, erm, "spirited" review, we're assuming you're one of those goats on the roof of Al's Swedish Restaurant in Door County...

Well, how'd we do? (Keep 'er PG for cripe's sake!)

• 🧀🧀🧀🧀🧀 Made quite the splash!

• 🧀🧀🧀 Had a great time, just need a little sunscreen

• 🧀 Aw, cripes! You dropped my bratwurst in the sand