In 1975, a young man claimed to have been bitten by a bull shark in Lake Michigan, but his account was later determined to be a hoax that was inspired by the movie Jaws, which was released the same year. Rumors have long persisted in the possibility of a bull shark swimming up the Mississippi River from the Gulf of Mexico and navigating its way into Lake Michigan. Others have suggested that it may be easier still for a shark—a shark capable of swimming in freshwater like the man-eating bull shark—to lurk along the St. Lawrence Waterway, making its way into the Great Lakes system.
Scientists are skeptical that a bull shark would find its way into the lakes, much less be inclined to attack human swimmers. These days, it would be next to impossible for a bull shark to make its way past the locks and dams of the Mississippi to reach Lake Michigan much less tolerate the colder waters of the St. Lawrence.
Even the northern reaches of the Mississippi would be much too cold for a bull shark to traverse. By the time the shark made it up the 2,000 mile stretch to the lake, the weather would have shifted, making the water temperature too cold for even the hungriest bull sharks. Though shark enthusiasts point to the fact that bull sharks have swum up the Amazon River for some 2,000 miles, the climate there is far more conducive for up-river navigating than what one finds in North America.
Of course, just because bull sharks are unlikely to reach Oak Street Beach doesn’t mean one won’t encounter them in the Midwest. Not only have there been accounts of bull sharks spotted in the Ohio River north of Memphis, they’ve been documented as far north as St. Louis.
In fact, National Geographic has reported on the sharks swimming further up river still to Alton, Illinois. During the 1930s, two fishermen caught a five-foot bull shark where it was swimming near Alton.
According to National Geographic, these sharks may exceed seven feet in length and weigh roughly 300 pounds. Unlike most sharks that require saltwater environments, bull sharks frequent freshwater rivers with outlets to the sea. They have a notorious reputation for attacks on humans, particularly in rivers such as the Ganges of India and the Zambezi in Africa.
While most bull shark attacks occur in tropical or subtropical waters, the species does wander northward during the warm season–and some researchers have suggested that the trend for northward swimming may be increasing with global warming. In 2005, shark teeth were pulled out of Minnehaha Creek in Minnesota; scientists were able to confirm that the teeth once belonged to a juvenile bull shark.
In 2010, a juvenile bull shark washed up on a boat ramp in Olmsted, Illinois from the Ohio River, which flows into the Mississippi near Cairo, Illinois. Scientists believe that the sharks veer into the rivers in order to provide better cover for their young from predators. And while they are not commonly found to the north of St. Louis, they do not exactly teem in the waters of the southern Mississippi River either. People have a greater chance of drowning in the waters of the Mississippi than being attacked by a bull shark while swimming.