Because they're fresh water. Because they're not seas. First of all lakes are vastly smaller than seas, some which are large enough to encompass or surround larges bodies of land. Also lakes are freshwater.
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While lakes are fully surrounded by land, a sea is only partly surrounded by land, according to National Geographic(Opens in a new window). The Caspian Sea is fully surrounded by land, but it contains saltwater, which is not typical for lakes. However, it's by no means the only saltwater lake in the world.
The United States Environmental Protection Agency, for example, describes them as “vast inland freshwater seas.” A seminal 2017 paper in Limnology and Oceanography, authored by some of the most influential researchers studying the lakes, also refers to them as 'inland seas.
Lawrence Seaway is a deep draft waterway extending 3,700 km (2,340 miles) from the Atlantic Ocean to the head of the Great Lakes, in the heart of North America.
While there have been past “sightings,” most have turned out to be pranks or misidentifications. The reality is that the largest of the Great Lakes (Lake Superior and Michigan) are extremely deep lakes that are too cold for sharks.
Geology of Lake InferiorLake Inferior is an underground lake that is located beneath Lake Superior. It is believed to be formed by a process known as karstification, which is the dissolution of limestone and dolomite rock. This process creates sinkholes, caves, and underground rivers and lakes.
Exorheic, or open lakes drain into a river, or other body of water that ultimately drains into the ocean. Endorheic basins fall into the category of endorheic or closed lakes, wherein waters do not drain into the ocean, but are reduced by evaporation, and/or drain into the ground.
However, dangerous currents may exist at any time near piers, breakwalls, and river outlets. Always use caution and never swim alone. A Moderate Swim Risk implies that breaking waves and currents are expected at the beach. Stay away from dangerous areas like piers, breakwalls, and river outlets at these times.
Dreyer is the only person who has swum the width of Lake Michigan between Wisconsin and Michigan, having swum from Two Rivers, Wisconsin, to Ludington, Michigan, in 1998. In the 2023 swim, he was attempting to beat his own record by swimming 25 miles further in the route from Milwaukee to Grand Haven.
Lake Superior's beaches are open and safe for swimming over 90% of the time, and the water is extremely clear, with an average underwater visibility of 8.3 m (27 ft).
But those new to the area may not know that underneath the waters of Millerton Lake was the original town of Millerton. According to the California Department of Parks and Recreation, Millerton Lake was created following the construction of the Friant Dam. But to create the lake, the town underneath had to be flooded.
Alligators are rarely found in the Great Lakes. Although some alligators thrive in freshwater, it's just too cold in the north for them to survive. They don't typically live farther north than North Carolina. It's unclear how the alligator arrived to Lake Michigan.
But Heithaus said it would not be possible for a bull shark to reach the Great Lakes on their own because most don't travel very far upstream. If one did reach the lakes, it would not be able to survive due to the cold water temperature.
These lakes are the perfect backdrop for swimming, boating, and other water-related activities. But there can be more danger in these Great Lakes waves than what you'd find in the ocean. The Great Lakes are more than capable of generating waves over 10 feet high, despite being smaller than our oceans.
The primary reason for shipwrecks on the Great Lakes is stormy weather, specifically in the upper portions of Lake Michigan, Lake Huron and Lake Superior. In the late fall and early winter, weather can be particularly treacherous. Most Great Lakes shipwrecks occurred in the late fall.