The fresh water of the earth is contained in lakes, ponds, rivers and streams. Lakes are large bodies of freshwater surrounded by land, while ponds are smaller bodies of water surrounded by land. For example, Lake Tahoe is a huge lake originating from mountain stream runoff. Most lakes are still and contain a diverse plant and animal life. Rivers and streams are moving bodies of fresh water which usually originate in mountains and come from melting ice or ground water and eventually terminate in oceans. For example, the Amazon originates in the Andes Mountains and ends in the Atlantic Ocean. Over time, as rivers travel, they change course and carve a place through land. This causes ox bow lakes, caverns, and canyons. Many animals live in rivers and lakes. Some need the movement of the water to survive. Estuaries are places where fresh and salt-water habitats come together.