The water temperature in the Great Lakes is far too cold for most sharks (including the Bull Shark). Even if it managed to make it through the summer months, our frigid winters would turn it into a “sharksicle” in no time.

No, a shark cannot survive in the Great Lakes for any meaningful length of time, and there are no native shark populations in these bodies of water. The Great Lakes (Superior, Michigan, Huron, Erie, and Ontario) are entirely freshwater ecosystems, which presents a fatal physiological challenge for almost all shark species. Sharks are saltwater fish that rely on a process called "osmoregulation" to balance the salt content in their bodies with their environment; in a freshwater environment, their cells would take on too much water, leading to a rupture and eventual death. While the Bull Shark is famous for its ability to swim into freshwater rivers like the Mississippi, it cannot survive the extreme cold of the Great Lakes, which often drop to near-freezing temperatures during the winter. Bull sharks typically require water temperatures above 70°F (21°C) to thrive. Furthermore, the locks and dams of the St. Lawrence Seaway act as physical barriers that prevent large marine predators from migrating into the lakes. Any reported sightings of "sharks" in the Great Lakes are typically cases of mistaken identity (often involving Lake Sturgeon) or internet hoaxes.