Sharks In Lake Michigan: True Story or Urban Myth? (2024)

As kids, we come up with some very unrealistic scenarios and bravely imagine how we would deal with them. One that I, and many others, dreamt up was a massive shark hiding in the deep end of the swimming pool.

See, the mind can play tricks on you, especially in water over your head. Those kinds of fantasy scenarios come back into mind when you can’t see the bottom, even as an adult.

So while there’s clearly no shark in the pool, what would you say if I told you you’ve probably swum with sharks in almost every other body of water?

Helicopter photos of beaches prove they’re quite close to people, but that’s expected. Unfortunately, there’s no real way to know if you’ve been around a shark in freshwater either, and not only is it possible, but depending upon where you are, it’s likely.

In this article, we’ll discuss shark sightings in Lake Michigan and other bodies of freshwater, go into detail about the validity of those claims and talk about the incredible sharks that do venture out of the oceans and into the rivers and canals in your backyard.

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Are There Any Cases Of Sharks In Lake Michigan?

Looking at cases of sharks species found in Lake Michigan is a bit of a slippery slope. There are a lot of reported sightings, at least when it comes to fins popping up out of the water.

For the most part, these are likely explainable without including sharks and have not been verified scientifically. In only one case was a shark actually found in Lake Michigan, and it was proven to be a hoax.

April 25, 1969. Two coho salmon fishermen pulled a 29-inch (73-centimeter) shark from the water around two miles off the coast of Milwaukee.

The body of the shark was found floating in the water and caused quite a stir around the fishing communities in the area. This case is also the main reason why there’s a dim memory of sharks being found in the lake.

The incident was very quickly disproved, however. A local bar owner caught the shark on a trip to Florida two years prior and had kept it in his freezer. He then had the fishermen plant the shark in the lake as a prank.

While there are all kinds of reports of sharks, alligators, and other potential pet animals being released into the lake, there has never been a documented case of any of these animals in Lake Michigan.

Those “unfounded” reports and a few historical hoaxes are the main reason people believe there are sharks in the Great Lakes.

Which Sharks Can Live In Freshwater and How Do They Do It?

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So when we’re talking about freshwater sharks, we don’t mean the ones at the pet store that are called sharks. Those fish are small species of cyprinids and catfish that get mislabeled to help their value in the aquarium trade due to their body shapes.

There are definitely more true sharks that can survive in freshwater than you think.

Realistically, most sharks can tolerate fresh water for very short amounts of time. You’ll find all kinds of sharks going up into shallow bays and estuaries in search of prey or to give birth to their young.

When it comes to pure freshwater, 43 species in the elasmobranch family have documented sightings. The bull shark appears most often and is the best known, but species of stingrays and sawfish frequently enter rivers. Some types of sandbar sharks, smooth dogfish, and skates enter estuaries often as well.

There are four species of shark I’ve found you’ll often find in freshwater environments. The bull shark is again the most common, but river sharks also exist.

Bull sharks are ocean-going predators that enter rivers and estuaries in search of food and to find good places for their young to start their lives. River sharks spend most, if not all, of their lives in freshwater.

Glyphis sharks, the only true freshwater sharks, are those river sharks. Today, there are only three known species in the genus, the Ganges shark, the northern river shark, and the speartooth shark.

The Ganges shark is restricted entirely to freshwater environments, while the other two are found in the coastal waters of their regions as well.

All of them have very secretive habitats, live in poor visibility rivers, and aren’t very well-studied. It’s assumed all of them are critically endangered, though we just can’t say for sure. There could be more species out there too, but we haven’t found them yet, and the ones we know about are exceptionally rare.

Wait, Then What’s Stopping Sharks From Getting to the Great Lakes?

A lot, actually. While bull sharks have been spotted as far up the Mississippi River as St. Louis, that doesn’t mean they can physically get to any of the Great Lakes.

In terms of salinity, I don’t see why bull sharks couldn’t make it up there. The entire length of the Mississippi River is around 3,766 kilometers (2,340 miles), and bull sharks have been found 4,000 km (2,500 mi) up the Amazon River in Peru. But it being freshwater isn’t the only factor to consider.

Going north up the Mississippi beyond the St. Louis area just isn’t really possible for bull sharks. There are just too many locks, dams, and other physical obstacles in the way.

Plus, to detour off the Mississippi River and reach Lake Michigan specifically, bull sharks would have to figure out a way to navigate over Niagara Falls.

Some animals have been able to make their way from the sea to the Great Lakes.

Sea lampreys are a prime example, but even they only made it all the way there after shipping channels were carved out so transport ships could get around Niagara Falls.

In short, it’s extremely improbable for bull sharks, or any other species of shark, to swim all the way into Lake Michigan. If there is one there, it’s never been scientifically documented, and they would probably die shortly after entering the lakes due to a lack of suitable food sources and cold winter temperatures.

For an awesome interactive map of all the obstacles facing a bull shark traveling to Lake Michigan, you can scroll around this link.

But that just covers the Mississippi River. The St. Lawrence River in Canada is known for having several different species of sharks, including Great Whites, basking sharks, Greenland sharks, and porbeagles.

But that’s the thing. St. Lawrence may provide a direct channel into Lake Ontario and the Great Lakes as a whole, but the sharks that live there rarely even reach Quebec City. It widens out as it nears the ocean, resulting in a mixture of the freshwater from the Great Lakes and the salty water of the Atlantic Ocean.

The water is also too cold for sharks like bull sharks to reach the lakes this way. The Mississippi River is a viable option for bull sharks, but they can’t make it past the obstacles we already discussed.

If you look at the glyphis sharks, you’ll note all of them are native to the Indo-Pacific regions of Asia and Australia, with no chance of ever swimming over and entering the Great Lakes.

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How Bull Sharks Evolved To Survive In Freshwater Environments

Marine animals entering freshwater isn’t as uncommon as you might think.

Many species that are commonly known to do so are called diadromous. Salmon and tilapia are two you’ve probably heard of when it comes to fish moving between fresh and saltwater.

Bull sharks are both diadromous and euryhaline. Euryhaline is a term that means a species that can tolerate a wide range of salinities, from pure freshwater to saltwater and every brackish salinity level in between. But how exactly do bull sharks do it, and why do they bother?

All members of the shark/ray/skate/etc. family typically have blood that remains the same salinity as their environment. It’s the reason why saltwater fish die in freshwater and vice-versa.

Their bodies can only properly operate when their blood is the proper salinity and moving out of water containing that balance is enough to kill them. See, fish lose or absorb salt as they take water in from their gills.

Sharks have organs that help regulate the amount of salt in their body, which builds up in their bodies in the form of urea especially. The rectal gland, kidneys, liver, and gills all help regulate the amount of salt in the bull shark’s body.

In the open ocean, sharks use most of these to expel or take up salt, but the bull shark can do a few special things to stay regulated. To explain it as simply as possible, bull sharks can decrease the amount of salt they let go of while in freshwater.

When a bull shark enters a less-salty body of water, their body just changes the way it regulates salt to let them survive in a different salinity.

Bull sharks can live their entire lives in freshwater if necessary, but they typically won’t do it. That’s why finding them so far up rivers isn’t a problem. They can leave or stay as long as they like, as long as they have enough food.

So why do bull sharks go into freshwater in the first place? It’s a major evolutionary advantage, but adult sharks would have an easier time finding large meals in the ocean.

Bull sharks give birth in freshwater. There are fewer predators for their young and plenty of food for juveniles. Rivers, estuaries, swampy areas, and lakes are all fair game for them if they can get back to the ocean.

From the bayous of Louisiana to Lake Nicaragua, bull sharks are found far away from the actual ocean, leading to some interesting competition between predators.

Most young bull sharks can’t tolerate high salinities. They’re born in fresh or brackish environments and gain better tolerance as they age.

Older, large bull sharks have a higher tolerance for salty water and are most often found in the ocean where there is enough food to sustain them. They still keep the ability to go into fresh water whenever they wish, though they usually only do it for breeding.

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