Smith: There are more than 15,000 lakes in Wisconsin. What are the state's deepest lakes?

If you've spent any time in Wisconsin you know the state is blessed with lakes.

How many? The "documented" number is 15,074, according to Wisconsin Lakes, a publication of the Department of Natural Resources.

The lakes range from 1-acre spring ponds to 137,708-acre Lake Winnebago.

And that doesn't include the Great Lakes of Michigan and Superior on our eastern and northern borders, respectively.

Covering 31,700 square miles and with a maximum depth of 1,332 feet, Lake Superior alone contains 3 quadrillion gallons of water, enough to flood all of North and South America to a depth of 12 inches, according to the Alliance of Great Lakes.

Each of the Badger State's 72 counties has at least a handful of lakes, ranging from Green County (five lakes) to Vilas County (1,318).

With rich traditions of outdoor recreation and cabin life, lakes are part of our Wisconsin identity.

But it's not as easy to know what's beneath the surface.

And thanks in large part to glacial activity thousands of years ago, many of our lakes are very deep.

That's a good thing for several reasons, said Eric Olson, director of Extension Lakes, a UW System program housed at UW-Stevens Point.

Lakes with higher volumes of water tend to better withstand land use changes around them, Olson said. In a nutshell, big, deep lakes tend to have clearer water.

"People like it, you can see your toes when you're swimming," Olson said. "It's good for the native fish and other animals, too."

The deepest natural, inland lake in Wisconsin is Big Green Lake

What are Wisconsin's deepest lakes?

When it comes to natural, inland lakes, Big Green Lake in Green Lake County takes the blue ribbon. Big Green has a maximum depth of 236 feet.

Stephanie Prellwitz, chief executive officer of the Green Lake Association, said the lake was formed about 15,000 years ago when a retreating glacier blocked a deep valley which subsequently filled with water.

The central Wisconsin lake has drawn humans to its shores for hundreds of years, from Native American tribes to more recent generations of visitors and homeowners.

In her 2021 UW-Madison master's thesis on Big Green, Rachel Johnson said the Ho-Chunk people called the lake Te Čo or Ti-cho-ra for its changing green blue color.

That clear-water association is true to this day.

"(Big Green) stands out in so many regards," Prellwitz said. "And because of its depth and volume it has been able to sustain better water quality in the face of challenges facing all lakes."

Phosphorus entering the lake is one of those issues, as well as a mid-layer dead zone that sets up each year.

The top five deepest natural, inland lakes in Wisconsin

But Big Green has a good fishery that includes lake trout and cisco, two native Wisconsin fish found only in the deepest lakes.

The Green Lake Association is working to address environmental issues and to improve the health of the lake's ecosystem.

"We know what a gem we have in the state's deepest lake," Prellwitz said. "It's worth fighting for."

Geneva Lake in Walworth County is the second deepest natural inland lake at 135 feet. It is also a remnant of glacial activity.

Rounding out the top five are Elkhart Lake in Sheboygan County, 119 feet deep; Trout Lake in Vilas County, 117; and Beaver Dam Lake in Barron County, 106 feet.

What about the deepest artificial lakes in Wisconsin?

If artificial lakes were included the list would look different.

The deepest then would be Lake Wazee, a former iron mine in Jackson County at 350 feet in depth. Wazee made news in 2015 when a DNR fisheries survey there netted a 17.5-pound walleye, just a cisco meal shy of the 18-pound state record.

Wazee is stocked periodically with trout, and a cisco introduction project was started in 2013. And due to electric motor-only restrictions, the lake doesn't get much fishing pressure. But it's cold, deep waters are clearly able to sustain some fish.

Two quarries that filled with water are also very deep, according to the Wisconsin Lakes inventory: Redgranite Quarry in Waushara County at 163 feet deep and Lohrville Quarry in Waushara County at 120 feet deep.

Olson of Extension Lakes said it's possible another very deep artificial lake will make the list in coming years due to quarry or other activity. But the deepest natural lakes are pretty well set.

"Scientists have been able to catalog our natural lakes thoroughly for things like depth," Olson said. "As well as it's known, it still provokes a sense of wonder at how many big, deep, natural lakes we have in Wisconsin. It really sets our state apart in that regard."

This article originally appeared on Milwaukee Journal Sentinel: What are Wisconsin's deepest lakes?