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A watershed is an area of land that drains to a river, lake, or ocean. Hills organize the land into different watersheds. When rainwater hits the ground, mountain and hill ridges channel runoff water and groundwater (water that has soaked into the ground) into water bodies, such as streams and rivers. Because all runoff and groundwater will eventually flow somewhere, every land surface is part of a watershed. As water flows over land surfaces it picks up particles, nutrients and pollution that drain with the water into rivers, lakes or oceans. Watershed science is therefore an important part of remedying problems, such as pollution, that may affect a particular body of water.

Massachusetts has 28 distinct watersheds that feed six larger river basins. A river basin includes all the land drained by a river and its tributaries. The Connecticut River drains nearly one third of the state - the land between the peaks of the Berkshires and the Worcester Plateau. The Housatonic River and its tributaries drain most of the land west of the Berkshires. East of the Worcester Plateau, watersheds feed the Charles River, the Merrimack River, and many smaller rivers that ultimately make their way to the coast.

Watersheds do not conform to political boundaries, so often it does not make sense to focus on a portion of a river that lies within a particular city or county. Managing a watershed as a whole achieves better conservation strategies that work with the natural layout of the land. Cooperation increases the ability of organizations to effectively handle watershed problems, which in turn leads to better economic and scientific management of the river and its watershed. CRWA strives to protect the Charles River by promoting this cooperation between diverse organizations, communities and levels of government.

Everyone has a watershed address. Find out which watershed you live in by visiting the EPA's Surf Your Watershed site.

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• The Charles River is 80 miles long and flows directly through 23 towns and cities in eastern Massachusetts, beginning at Echo Lake in Hopkinton and ending in the Boston Harbor.
  
  
• The Charles River drains an area 308 square miles (its watershed). A watershed is the area that drains into a river, lake or harbor.
  
  
• 35 towns and cities comprise the Charles River watershed.
  
  
• The Charles River has 19 dams along its length.
  
  
• Today’s Lower Basin of the river was created when a dam was built in 1910 where the Museum of Science is today. This dam eliminated the mud flats and marsh land surrounding the Charles and stabilized water flow. Locks at this dam are an important barrier to salt water intrusion from the ocean.
  
  
• The Charles River drops approximately 350 feet as it travels to the sea.
  
  
• There are 20 species of fish found in the Charles River, including two species of River Herring - Alewife and Blueback Herring - that are anadromous, or migratory, and swim upriver from the sea to spawn (lay eggs) each spring. These fish must climb a series of fish ladders set up at each of the lower five dams on the river.
  
  
• The Charles River watershed is the most densely populated watershed in New England.
  
  
• More than 8,000 acres of wetlands in the Charles River Watershed have been protected forever from development as part of the Natural Valley Storage Project undertaken by the US Army Corps of Engineers in 1974.
  
  
• The Esplanade, part of the MA Department of Conservation and Recreation's Charles River Reservation, hosts more visitors than any other riverfront park in the nation.
  
  
• A variety of boats can be seen on the Charles River: power boats, sailboats, sculls and other rowing shells, wind surfers, canoes, kayaks, pedal-powered boats, solar-powered boats, boats made of recycled materials, rafts, and inner tubes.

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