Waters Held by the Land: Lakes, Bays and Fjords

Lake Baikal opens the path as the deepest lake on Earth, reaching 1,642 meters, in a tectonic rift in southern Siberia. Its basin is thought to be more than twenty-five million years old, and that long isolation is why so many of its species live nowhere else.

The Great Lakes are five connected lakes, Superior, Michigan, Huron, Erie and Ontario, that together cover about 244,000 square kilometers and reach a depth of 406 meters. Glaciers carved and dammed their basins, and they drain through the St. Lawrence River to the Atlantic, so they form a single shipping corridor between two countries.

Lake Chad is the shallow counterpoint to Baikal, with a maximum depth of only about 2 meters. It has no outlet to the sea, it sits where Chad, Niger, Nigeria and Cameroon meet, and its area fell from about 25,000 square kilometers in 1960 to roughly 2,000 by 1980, showing how a lake this shallow responds to changes in its supply.

The Dead Sea lies on the border of Israel, the West Bank and Jordan, with a shore about 430 meters below sea level, the lowest point on the surface of the continents. Fed mainly by the Jordan River and with no outlet, it has become far saltier than the ocean, and upstream diversion has lowered its level by roughly a meter a year.

Chesapeake Bay is the largest estuary in the United States, about 320 kilometers long and covering 11,601 square kilometers. It formed when rising seas flooded the valley of the Susquehanna River roughly 10,000 years ago, which is why a water body this large is only about 6.4 meters deep on average.

The Gulf of Mexico is much larger and deeper than the bay before it, about 1,550,000 square kilometers, bounded by the United States, Mexico and Cuba. It is mostly enclosed by land yet joins the Atlantic through the Straits of Florida and the Caribbean through the Yucatan Channel, and it is one of the largest offshore petroleum regions in the world.

Milford Sound sits in Fiordland National Park on New Zealand's South Island and is about 15.1 kilometers long. Despite the name, geologists classify it as a true fiord, because glacial erosion cut it, and it reaches a depth of 291 meters in an area of only about 25 square kilometers.

Scoresby Sund on the east coast of Greenland closes the path with the same glacial process on a far larger scale: a branching system of fjords covering about 38,000 square kilometers and reaching 1,450 meters deep in places. It opens into the Greenland Sea and has a single permanent settlement, Ittoqqortoormiit.