First a primer about what's the difference between a lake and a sea. While "sea" is a general designation for all the salt water in all the oceans, it's also the name associated with bodies of salt water that are partially landlocked, like the Red Sea. "Sea" is used as well to designate inland bodies of salt water, such as the Aral Sea, and sometimes even inland bodies of fresh water, for example the Sea of Gallilee. A lake is considered to be a large, inland body of fresh water, though, no distinction is given as to exactly how large a body of water must be to be a lake. For our purposes, we'll say that any inland water body is a lake, regardless of whether it contains fresh or salty water.

North America can lay claim to some pretty impressive lakes. For instance, Lake Superior has the greatest surface area of any fresh water lake in the world. Crater Lake (Oregon) is one of the deepest lakes in the world, and Great Salt Lake (Utah) is one of the saltiest water bodies. But lakes in other lands also have some unique characteristics. In South America, Lake Titicaca, in the southeastern corner of Peru, is the world's highest navigable lake, lying 12,500 feet above sea level! Africa's largest lake is Lake Victoria, and the world's second largest fresh water body. It's perhaps one of the most scenic lakes in the world, straddling the Equator and forming part of the borders of Uganda, Kenya and Tanzania.

If travel plans take you to Antarctic, you'll be near the world's coldest lake, Lake Vostok. However, since it's buried beneath several thousand feet of glacial ice, you won't actually be able to visit it. Discovered just 5 years ago, it's one of the largest lakes in the world - its exact size is still not known. Cut off from the rest of Earth for at least a million years, Lake Vostok may harbor previously unknown species of microbes, having the ability to withstand conditions at the edge of survivability.

The distinction of the world's lowest and possibly the saltiest lake goes to the Dead Sea. Bordering Israel and Jordan, it lies 1,340 feet below sea level! Asia can claim the largest inland water body in the world, the Caspian Sea, and it's smaller neighbor to the east, the Aral Sea, has the infamous claim of being the world's fastest disappearing large water body. Two decades ago it was the 4th biggest body of water on the globe, but now, it's in 9th place.

Even though these lakes and seas are indeed noteworthy, the subject of this week's question has been referred to as the "blue eye of Siberia," Lake Baikal in eastern Siberia. This crescent-shaped lake is more than 900 miles from the nearest ocean (the Pacific) and is about 400 miles long and 50 miles wide. Rimmed by mountains, and nearly surrounded by forests, it's one of the most beautiful lake settings in the world. While it's the 7th largest lake on the globe in regards to surface area, in terms of volume of water, Lake Baikal has no peers. Its greatest depth is 5,022 feet - the world's deepest lake.

Interestingly, Lake Baikal is gradually getting bigger. It rests in the biggest continental trough or rift in the Earth's surface, and this rift has been widening at a rate of about 3/4 inch (2 cm) per year. Lake Baikal is so astonishing big that if were drained, and if all of the world's rivers were diverted so as to empty into the huge trough, it would take a full year to refill it! Not only does Lake Baikal contains 1/5 of all of the world's supply of unfrozen, fresh water, but it could satisfy the drinking water needs of everyone on Earth for almost 50 years.

Though more than 330 rivers and streams feed Lake Baikal, only the Angara River is an outlet. The Angara empties into the Arctic Ocean, more than 1,500 miles away. Lake Baikal is estimated to be nearly 25 millions years old, making it possibly the world's oldest lakes. Additionally, of the 1,800 or so fauna and flora that are found in and around the lake, about 2/3 of them are indigenous - a higher percentage anywhere, except for the Antarctic lakes. While most of the lake's unique fauna are microscopic invertebrates, the Baikal seal is one of the lake's most popular indigenous mammals.

Unfortunately, Lake Bailkal's once pristine waters are no longer that way, but even though the water is now tainted by pollution, it's still remarkably clear. Tiny crustaceans act to purify the lakes's waters so that it's possible to see a bright object on the lake bottom in 500 feet of water! However, while the lake water is still clear now, a real concern is that the buffering effect of the lake's well-oxygenated waters may be overwhelmed by toxins and industrial waste in the near-future.

Until timber began to be widely harvested from Lake Baikal's slopes in the early 1900s, it's said that the lake's water was clean enough to be consumed without filtering. As large tracks of forests were removed with the growth of lumber and pulp industries, tons of silt and sediment washed into the lake. Since the 1960s, industrial pollution has been the biggest problem. More than 100 factories can be found close by the lake. Perhaps the worst polluters are factories that use chlorine to turn wood pulp into cellulose, which is used in the manufacturing of cardboard packaging. This chlorine slowly but surely makes its way into the lake. As a result of this chemical pollution, not only have some fish species declined but so have smaller life forms that are crucial in keeping the lake healthy. Pollution from the largest cites near the lake, Irkutsk to the southwest and Ulan Ulde to the southeast, are also causing problems. In addition, another source of pollution comes from the burning of coal in several power plants adjacent to the lake. Since Lake Baikal contains such a large volume of water, and only a single river outlet, the contaminants that are present now will be there for years to come.

A number of initiatives have been proposed over the years and a few laws have been passed to prevent blatant pollution practices. However, as of now, many of these laws have little bite. They may impede polluters but they can't stop them. The people who live near Lake Baikal, of course, don't want to see their beautiful lake threatened by pollution. A few groups are doing what they can to promote awareness of the lake's fragility and are active in efforts to remove litter and reduce industrial effluent. But, because the Russian economy has been in dire straits since the break up of the Soviet Union a decade ago, the government's emphasis has been on trying to fix the economy, and environmental issues receive relatively little backing, financial or otherwise. Closing down a lake-side factory in violation of pollution ordinances, and thus eliminating perhaps thousands of jobs, will just further cripple the region's economy. It'll be sometime before things get better. Even the few government and scientific institutes that in the past have been responsible for monitoring this impressive lake's health, now have few resources to do so.

For more about this see the March 1967 issue of National Geographic, the book, Realms of the Russian Bear by J. Sparks (BBC Books, 1992) and the Washington Post newspaper articles on Siberia (August 26-31, 2001).