The deepest lake on Minnesota shores is Lake Superior. However, the deepest inland lake in Minnesota isn't even really a lake.

Lake Superior's deepest point is 1,332 feet. It's the deepest of the Great Lakes, coldest, and best (That's why it's Superior). The deepest inland lake in Minnesota is 450 feet deep. Can you imagine swimming in that? It would feel like hovering over an abyss.

Here's the catch. It's not a real lake. It's an abandoned mine pit that has since become a lake. Portsmouth Mine Pit Lake is located near Crosby, Minnesota. It's part of the Cuyuna Iron Range.

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Google Maps

The mine eventually filled with water and became an artificial lake. You can actually see a video of the lake before it filled with water because there was an air and space mission that took place there in the 1950s.

The United States Airforce in the 50s began doing high-altitude balloon flight tests to observe how humans would react to a spaceflight. They were doing early work on the space program that eventually became NASA. One of those balloon flights took place at the Portsmouth Mine in 1957. It was called MANHIGH II. It launched from the mine and flew for over 32 hours at high altitude, at the edge of space. The highest point it reached was over 100,000 feet. You could make the argument that one of the first steps to the United States reaching space started in a Minnesota Lake.

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I didn't see a specific reason noted for why they chose the mine pit, but I imagine it probably helped with protecting the balloon and capsule from winds by being so far below ground.

But anyway, back to the lake itself. It's been stocked regularly with brook and rainbow trout. It's part of the Cayuna County State Park Recreation Area and has a campground on its west shore with a swimming beach. People often kayak and canoe and fish in the lake. This YouTube video shows a GoPro looking down into the water as the person kayaks across the pit.

It's also one of the many pits that divers like to explore in Northern Minnesota.

Which, reminds me of this creepy article where there's actually a Jason in the bottom of the Louise mine pit right next door. Spooky stuff!

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