Yellowstone National Park (YNP) supports one of the most significant aquatic ecosystems in the U.S. Headwater streams and rivers emerge from the park and join to become three of America’s most important waterways and ultimately flow into the Pacific and Atlantic oceans: the Yellowstone River, the Missouri River and the Snake River. At the heart of YNP lies Yellowstone Lake – the largest alpine body of water in North America. The park encompasses about 2.25 million acres, five percent of which is covered by water, including more than 220 lakes and 2,650 miles of streams.