Everyone learns this in elementary school, particularly if you grew up in Michigan - the names of the 5 Great Lakes and how to remember them. But what you leaned in school is wrong. There are only 4 Great Lakes.

You could very likely recite the names of the Great Lakes now, and if you did you likely remembered the acronym HOMES. Huron, Ontario, Michigan, Erie and Superior. That's them all right, the 5 Great Lakes. But in the most strict scientific scene, there are only 4.

Look at a map and you'll likely guess what the answer is.

Superior is clearly a lake unto itself separated from Lake Huron by the St Mary's River. Lake Erie is separated from Huron by the St. Clair River-Lake St. Clair-Detroit River and Lakes Erie and Ontario are separated by the Niagara River.

However the boundary between Lake Michigan and Lake Huron is no so cut-and-dry. The two lakes are joined by the Straits of Mackinac. A strait - not a river. The strait is 5 miles wide and 20 fathoms deep making it a waterway much wider and deeper than a river. Also, the straits help regulate the flow between the two bodies of water, making them one in the eyes of science. Lake Michigan-Huron, as it's properly known is

technically a single lake because the flow of water through the straits keeps their water levels in near-equilibrium. Combined, Lake Michigan–Huron is the largest fresh water lake by area in the world. Although the Straits create a pronounced bottleneck in the contours of the shoreline and a major constriction in the local bathymetry, defining two distinct basins, they are still deep and wide enough to allow the free exchange of water between the two sides. Because of the link through the Straits, Lakes Michigan and Huron have the same mean water level.

Another interesting fact about Michigan-Huron, the world's largest lake, is its residence time or the amount of time it takes for water to flow through the lake. In Michigan-Huron it takes water 100 years to flow through the lake.

So there it is. Just 4 Great Lakes: Michigan-Huron, Superior, Ontario and Erie.

[Wikipedia]