Baikal Seal, or Nerpa (Pusa sibirica), Zabaikalski National Park, Lake Baikal, Russia. The world's only freshwater seal, Nerpa are found only in Lake Baikal. Population may be declining; possibly a threatened species because of poaching. Lake Baikal is the oldest (25 million years), deepest (5700 feet), and largest lake in the world by volume (it holds 20% of the earth's liquid fresh water). Threatened by pollution and most recently by an oil pipeline, Baikal has become a rallying point for Russian and international conservationists. Baikal was declared a World Heritage Site in 1996. Boyd Norton, the photographer here, worked with Russian and U.S. environmentalists to get Baikal designated a World Heritage Site.