Lakes come in many varieties
The Earth has a tremendous variety of freshwater lakes, from fishing ponds to Lake Baikal in Siberia. Lake Baikal is the world's oldest, largest, and deepest freshwater lake. Nearly a mile deep and holding over 23, 000 cubic kilometers water, it would require the total volume of all the Great Lakes to fill it up if it were ever drained (NASA).
Most lakes contain fresh water, but some, especially those where water cannot escape via a river, can be classified as saline lakes. In fact, some lakes, such as the Great Salt Lake in Utah, are saltier than the oceans. Most lakes support a lot of aquatic life, but not all. The Dead Sea in the Middle East isn't called "Dead" for nothing —it is too salty for aquatic life! Lakes formed by the erosive force of ancient glaciers, such as the Great Lakes, can be thousands of feet deep. Some very large lakes may be only a few dozen feet deep—Lake Pontchartrain in Louisiana has a maximum depth of only about 15 feet.
Some of the salty lakes were formed in ancient times when they were connected to seas and when rainfall may have been heavier. These lakes have been shrinking since the last ice age. The ancient Lake Bonneville in the United States was once as big as Lake Michigan, and the Great Salt Lake was once about 14 times larger than it is now.