Discover The 10 Most Dangerous Animals Swimming In Ohio’s Lakes And Rivers

Ohio River
© Corey B Stevens/

Written by Sandy Porter

Updated: June 28, 2023

Share on:


Incredible, beautiful, lush waterways of Ohio welcome tens or even hundreds of thousands of visitors annually. With over 200,000 million tourists in the state each year, many folks make their way to the rivers and lakes to enjoy the natural beauty, catch glimpses of wildlife, and bask in the sun on the many shores.

With more than 100 natural lakes in the state, some of the largest lakes in Ohio include:

  • Salt Fork Lake
  • Atwood Lake
  • Caesar Creek Lake
  • Senecaville Lake
  • Buckeye Lake
  • Indian Lake
  • Mosquito Creek Lake
  • Shenango River Lake
  • Grand Lake St. Mary’s
  • Berlin Lake
  • Pymatuning Lake
  • Lake Erie

Many of these incredible lakes boast some of the loveliest and most inviting beaches of the Midwest, with amenities tourists the world over can appreciate.

Additionally, Ohio has several significant rivers flowing through, including:

  • Ohio River
  • Cuyahoga River
  • Grand River
  • Auglaize River
  • Black River
  • Blanchard River
  • Conneaut Creek
  • Great Miami River
  • Kokosing River
  • Little Muskingum River
  • Paint Creek
  • Sandusky River
  • Scioto River
  • Stillwater River
  • Tuscarawas River

All throughout the state, dangerous animals in Ohio’s lakes and rivers lurk.

Are Ohio’s Lakes And Rivers Dangerous?

Lake Erie in Lorain, Ohio

©Lake Front Drones/

The various bodies of water around Ohio pose various risk levels. River currents, for example, run fast and strong in the Ohio River, making it generally not the safest place to swim. Floating and submerged debris in the various rivers and lakes also may pose threats of danger. Commercial and private boating traffic may also be dangerous.

Algal bloom, however, is perhaps the biggest threat in several of the bodies of water around the state. Numerous programs exist to help mitigate the problem, monitoring the water of the Ohio River and others, but in many cases, restrictions are placed on the waterways and swimming, or other activities are not permitted.

A List of the Most Dangerous Animals In and Near the Major Rivers and Lakes of Ohio

And then, of course, there are the animals, some of which are quite dangerous, even deadly, while others may cause severe injury, illness, or painful encounters.

Predators of many varieties, along with dangerous reptiles, insects, and others live in and around the bodies of water in Ohio. The occasional rare exotic animal has been spotted as well, but there’s always an incident behind these encounters.

Let’s look at the most dangerous animals in Ohio’s lakes and rivers and the surrounding areas.

White-Tailed Deer (Odocoileus virginianus)

white-tailed deer

White-tailed deer are the deadliest animals in the United State. They frequently live near Ohio’s lakes and rivers and cause car accidents.

©Tom Reichner/

While “venomous snake” or even “snapping turtle” sounds more dangerous that the fluffy-tailed four-legged animal, deer are actually the number one wildlife killer of human beings in the United States. The timid, non-aggressive animals may weigh between 150 and 400 pounds, meaning they’re got some heft to them. The speed at which humans approach in vehicles and the sheer, lean weight of the mammals makes for a deadly combination. White-tailed deer are known to cause somewhere around 20,000 car accidents each year, resulting in human deaths between 120 and 200 annually.

Deer frequently come up out of water sources. They must live nearby water to remain hydrated, so their habitats usually involve a river, lake, or stream. If you’re just sitting at the water’s side, you may witness deer coming up for a drink or even a swim, or possibly passage across the water. In these settings, the deer are non-aggressive and won’t harm you.

However, frequently folks encounter the animals on roadsides near the water sources. Accidents occur, and sometimes death.

Sport Fish or Freshwater Fish

Bluegill underwater in the St. Lawrence River in Canada. The bluegill has a bluish tinge of scales on its face.

Bluegill is one of the few fish you can eat twice weekly from Ohio’s lakes and rivers. More often, though, could be deadly.

©RLS Photo/

Fishing is a hugely popular sport in Ohio. Fish are high in protein, low in fat, and contain healthy nutrients, such as omega-3 fatty acids. This makes them a favorite meal for many folks. Catching them can also be an extremely rewarding hobby, filled with exhilaration and a sense of accomplishment. However, the freshwater fish species of Ohio have some restrictions you’ll need to keep an eye on.

Most species of fish found in Ohio are deemed safe for consumption a single time per week and no more. Why? Because of low-level mercury contamination. This advisory is in place to protect humans from over-consuming the toxin which may kill us otherwise. Yellow perch and sunfish (bluegill, longear, redear) may be eaten twice weekly. Northern pike, Steelhead trout caught in Lake Erie and tributaries, and Flathead catfish over 23 inches should only be eaten once monthly.

If you eat the fish here more frequently, you could develop neurological and behavioral disorders. Tremors, insomnia, memory loss, headaches, motor and cognitive dysfunction, and neuro-muscular effects follow, with lifelong effects. And yes, mercury poisoning may even lead to death.

Eastern Massasauga Rattlesnake (Sistrurus catenatus)

Closeup of coiled massasauga rattlesnake

Massaugas are more likely to be found on land, but they are definitely a threat on the shores of Ohio rivers and lakes.


Though the snake is on the endangered species list, the Eastern massasauga rattlesnake is ranked among the top 10 most dangerous animals in Ohio. They rarely attack humans unless provoked or threatened, but when they do, their venom is deadly. The venom takes hold and kills within a matter of only 3.5 hours, unless antivenom and proper medical care are offered immediately.

The Eastern massasauga rattlesnake prefers damp lowlands in the forests and wet prairies. It’s often found in swampy areas, bogs, and marshes near major waterways throughout Ohio and other regions in the United States.

The snakes have shiny black scales with white stripes on their sides. Typically reaching 20 inches in length in maturity, they have 4 to 6 rattle buttons on their tails. They primarily feed on salamanders, squirrels, rabbits, mice, insects, and other small creatures.

If you are bitten by a snake of any kind, you should immediately seek out medical attention. If possible, call in a professional from the state to capture and bring in the snake for verification, but never attempt to catch such a reptile yourself.

Timber Rattlesnake (Crotalus Horridus)

Timber Rattlesnake coiled on a rock

Timber Rattlesnakes are some of the dangerous animals in Ohio’s lakes and rivers.


The Eastern massasauga rattlesnake isn’t the only venomous reptile in Ohio. It’s not even the only rattlesnake. You’ll also find Timber rattlers here. These venomous snakes frequently swim in and live around fishing ponds, lakes, and rivers of Ohio.

The Timber rattlesnake is exceptionally well camouflaged and often goes unnoticed until it’s too late. The coloring of the snakes allows them to disappear into the natural habitat all around waterways of Ohio. Gray snakes with rows of darker gray or black squares cover their backs.

Growing up to 3 feet in length on average and weighing in at as much as 25 pounds, these are fairly large snakes. Occasionally, the gray scales have a pinkish hue. They bear stripes down their backs in orange, pinkish, or yellow colors, while others have black or brown stripes. Each Timer rattler has buttons on the tail that make the rattle to sound off to predators. The snakes have been known to reach seven feet in length, though this is rare.

Despite their reputation, Timber rattlers are actually among the most docile of rattlesnakes. They rarely strike, though will when they feel it necessary. They’re more likely to stay stretched out or coiled, motionless when they are encountered in the wild. They are technically pit vipers, meaning their venom is deadly.

Timber rattlesnakes are primarily terrestrial, but they may also be found in trees as high as 80 feet tall. Their preferred food sources include small to medium-sized rodents like chipmunks, squirrels, and mice, along with lizards, birds, and amphibians. They ambush their prey from the brush, quickly striking and biting, injecting venom into the victim.

The Timber rattlesnake is not native to Ohio but has migrated in over time for various reasons.

Northern Copperhead (Agkistrodon contortrix)

Northern Copperhead (agkistrodon contortrix mokasen) on leaf litter - taken in New Jersey. Its ground color is pale brown to pinkish-brown, and it has darker, hour-glass shaped bands down its body.

Northern Copperhead (agkistrodon contortrix mokasen) – they don’t swim frequently, but they are found near the waters of Ohio on the regular.

© Kenny

Another venomous snake living frequently near bodies of water is the Northern Copperhead. They may occasionally swim in the water sources, but they’re far more often found resting or hunting nearby. This species lives in many states across the country, usually near rivers and lakes.

Like many other species of snake, Northern copperheads prefer to live alone and do not want to be bothered by humans. They don’t seek humans out, either. They are less likely to strike than more aggressive species, but if they feel threatened, they will. If you see a Northern copperhead, move away from them without provoking them and you’ll likely be fine. Bites are far more frequent when copperheads are taken by surprise than if they simply see a human.

The medium-sized, stout-bodied snake is covered in beautiful patterns of hourglass-shaped designs, the narrowest part usually along the spine. The coloration is brown to orange, helping them blend into their natural environment. Northern copperheads have pale-colored upper lips visible from a distance.

Watersnakes are frequently mistaken for them (and are harmless), so do not assume the snake you run across is nonvenomous. Somewhere around 8000 persons are bitten by venomous spiders annually in the United States, some of the bites leading to death. Watersnakes have barred or dark upper lips, though, and may be distinguished from copperheads in this way. It’s always better to assume the snake you encounter could be venomous, though, and move away as easily and quickly as you’re safely able to do.

Young or baby copperheads are typically gray or brown colored with bright yellow or green tail tips.

Interestingly, Northern copperheads are nonaggressive but are the most frequent venomous snake bites reported annually to the CDC. Their bites may be deadly, though rare. Instead, they are the least toxic bites of venomous snakes in the United States. Recovery from a copperhead bite requires antivenin therapy in some cases, but usually not. Again, it is better to assume you will need the antivenom and seek immediate medical care if you are bitten.

Copperhead bites occur most frequently because the snake remains motionless when it has come into the presence of humans or other large mammals. The camouflage of the animal is its primary protection. Bites occur when they are stepped on or accidentally grasped in the wild (or gardens) because humans simply don’t see them.

The typical diet of a Northern copperhead consists of small mammals and amphibians, as well as cicadas and caterpillars and other insects.

Wild Boars (Sus scrofa)

Group of wild boars, feral hogs

Wild boars are competent swimmers and may be found in the waters of Ohio lakes and rivers.


While the wild boar is far more associated with the islands of Hawaii or the forests of Texas, these feral pigs very much do exist in Ohio. They pose a huge threat to both crops and livestock and they also are extremely dangerous to humans.

Approximately 500 to 1000 wild boars roam the wild in Ohio (many having originally escaped farms or fled game hunting camps). Spread across 26 of the 88 counties in Ohio, wild boars may well be spotted while you’re out on the lake or riverfront.

Headlines frequently sensationalize wild pig attacks, but that doesn’t mean they aren’t dangerous. In fact, wild pigs often attack completely unprovoked. The attacks usually result in trampling or bites, which may cause other issues, but the attacks are rarely deadly.

The smaller number means you’re less likely to see wild boars around the lakes, but if you do spot some, never approach them. They are aggressive and do not need to feel threatened in order to attack.

Common Snapping Turtle (Chelydra serpentina)

Snapping Turtle by the water

Smaller snapping turtles are frequently seen sunning themselves. Larger specimens usually lurk toward the bottom of Ohio lakes.

©, CC BY 2.0, via Wikimedia Commons – Original / License

Ah, turtles! So friendly, so cute! Well, with the exception of the common snapping turtle found in the waterways of Ohio and other states. These reptiles may grow as large as 20 inches and weigh up to 20 pounds when fully grown.

That may not seem that dangerous, but when you consider that these turtles swim in the water, climb around on hidden debris, and easily blend into the habitat, they become a little more concerning. With powerful jaws designed to crack through the shells of other turtles, they’re a large threat to swimmers and fisherfolk who have exposed limbs in the water.

Common snapping turtles roam the water and land silently and solo. They’ve been reported to snap off fingers and cause other injuries to humans. The bites aren’t fatal in and of themselves, but they may result in loss of fingers and toes, and infections could enter the wounds and cause some serious harm.

Larger specimens are prone to hanging out at the bottom of rivers and lakes, but smaller ones rise to the surface and may frequently been witnessed basking on logs and rocks.

Channel Catfish (Ictalurus punctatus)

Channel catfish

Channel catfish have some nasty barbs that can lead to complications.

©Aleron Val/

Though rumors, after the Silver Bridge Collapse of 1967 claim channel catfishes swimming in the Ohio River, were large enough to swallow entire humans, no official confirmations of the fish reaching that size exist. However, they do bear venomous barbs, like most catfish species, that can cause some issues for humans. Channel catfish have been recorded as large as 58 pounds in Florida, with the largest in Ohio weighing at 37 pounds.

These fish are extremely common in the waterways of Ohio. They’re often caught by anglers and brought home as food. They have barbs filled with proteins in them that inject into humans when they sting. This is a protective measure by the fish to avoid being captured or killed.

In most cases, the proteins are harmless and just sting a bit. However, many incidents have occurred in which people have been pricked by the barbs and then experienced severe pain. Complications of secondary infections and other issues may arise, and full course antibiotics are required.

They are unlikely to kill if treated, but the stings of channel catfish will cause extreme pain and likely infections to follow.

Black Bears (Ursus americanus)

Black bear

Though they rarely attack, black bears are among the most dangerous animals found swimming in the waters of Ohio lakes and rivers.

©Joshua Daniiel/

Destruction of habitat and excessive hunting of black bears has largely driven these dangerous animals away from Ohio. And they are far more afraid of humans than they are intentionally aggressive towards them. Black bears are more likely to destroy a garden or wreck trashcans than attack people. But attacks are not unheard of.

They live near water sources to stay hydrated, of course, and you could easily come across them in the woods along a hiking trail near rivers or lakes. They do swim and catch fish, though you’ll rarely spot them in the water in Ohio. Attacks are nearly unheard of, though, with only one reported fatality annually in the United States. Generally, if you spot a black bear in the wild, you should slowly back away and walk away calmly. Running or trying to climb a tree is more likely to provoke the bear to chase or attack you.

Bobcats (Lynx rufus)

Bobcats enjoy going for a swim. Thankfully, they rarely attack humans.

Though they were once thought eradicated in Ohio, Bobcats have made a comeback and are among the most dangerous animals along Ohio’s waterways. They’re also highly competent swimmers and seem to enjoy frequently swimming. They typically hunt small mammals like rabbits and mice. They’re not particularly interested in humans, and, in fact, usually fear people. However, they have been known to come into campgrounds and urban areas. They rarely attack and must be provoked to do so. When they do attack, the results typically require a hospital visit to prevent infection and blood loss, but they rarely result in fatalities.

Share this post on:
About the Author

Sandy Porter is a writer at A-Z Animals primarily covering house garden plants, mammals, reptiles, and birds. Sandy has been writing professionally since 2017, has a Bachelor’s degree and is currently seeking her Masters. She has had lifelong experience with home gardens, cats, dogs, horses, lizards, frogs, and turtles and has written about these plants and animals professionally since 2017. She spent many years volunteering with horses and looks forward to extending that volunteer work into equine therapy in the near future. Sandy lives in Chicago, where she enjoys spotting wildlife such as foxes, rabbits, owls, hawks, and skunks on her patio and micro-garden.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.