LOCATION: Freshwater ecosystems include lakes, ponds, rivers, and streams. Lakes are large bodies of freshwater surrounded by land, while ponds are smaller bodies of water surrounded by land. Lake Baikal, in central Asia, is the biggest lake on Earth; it contains about one fifth of the Earth’s freshwater and has a maximum depth of 5,315 feet (1,620 meters)! Lake Tahoe is a huge lake on the border of California and Nevada that originates from mountain stream runoff. Most lakes are still and contain diverse plant and animal life. Rivers and streams are moving bodies of freshwater, which usually originate in mountains and come from melting ice or ground water and eventually flow into the ocean. For example, the Amazon River originates in the Andes Mountains and ends in the Atlantic Ocean. Over time, as rivers travel, they change course and carve a path through the land. This causes ox bow lakes, caverns, and canyons. The place where fresh and salt-water meet is called an estuary. A unique place where two habitats come together is called an ecotone. Because estuaries are usually shallow, sunlight can reach all levels of the water.