What is a Watershed?

A watershed is the land area off of which rain and/or snowmelt run off or “shed” eventually arriving into a receiving water body.  A “watershed” is sometimes referred to as a drainage basin.  You can define a watershed around a water body by following the highest points of land around that body of water. The scale of a watershed is relative to its receiving body of water, be it a river, stream, lake, pond or even a puddle in a parking lot.  There are watersheds within watersheds.

A watershed is a good geographic area by which to manage natural resources because the quality of the receiving water body will depend on the characteristics and use of the surrounding land.  Rain water and snow melt can pick up litter, sand, and chemicals as it runs off the land and can carry these pollutants into a receiving water body.

Paved or impervious surfaces “shed” more water and do so faster than non-paved surfaces.  Non-paved or pervious surfaces tend to absorb water like a sponge allowing rain water and snow melt to seep into the ground.  Examples of paved surfaces include roads, parking lots, driveways, sidewalks, and rooftops.  Examples of non-paved surfaces include lawns, forests, and fields.

Since a watershed is defined by water flow, not by political boundaries, it may transcend town and state borders.  Thus, communities may need to work together to protect the water quality of a receiving water body such as a river. The Commonwealth of Massachusetts coined the slogan “communities connected by water” when speaking of watersheds and the importance of working together to manage land resources and protect and restore water quality.  The State of Massachusetts is divided into 27 watersheds as defined around the State’s major rivers.

Do you live in the SuAsCo Watershed?

The SuAsCo Watershed is one of the 27 major watersheds in Massachusetts. SuAsCo stands for the Sudbury, Assabet, and Concord Rivers. The SuAsCo Watershed is the land area surrounding these three rivers. Any rain falling within the SuAsCo watershed eventually drains into the Sudbury, Assabet or Concord rivers.

The SuAsCo Watershed is a 377-square mile area encompassing, partially or wholly, 36 Massachusetts towns and cities. (see map) The three rivers of the SuAsCo Watershed connect these 36 municipalities as one community. Whatever happens in upstream communities will affect downstream communities and vice versa. For example, pollution upstream will impact the water quality of downstream towns, affecting their ability to use the river for drinking water or recreation. Or a dam downstream may impede fish migration to upstream towns affecting their recreational fishing and fish populations. Thus, the land use and water quality of the SuAsCo is best managed by working together as a watershed community.

Assets and Challenges of the SuAsCo Watershed

The SuAsCo Watershed boasts historic sites of national significance, such as the Old North Bridge, and is prominently featured in the works of the 19th century authors Hawthorne, Emerson, and Thoreau. In close proximity to metropolitan Boston, the Sudbury, Assabet, and Concord Rivers and their watershed provide a popular area for canoeing, fishing, hiking, biking, bird watching and other recreational activities. Seventeen miles of the Sudbury River, four miles of the Assabet, and eight miles of the Concord are federally designated as “wild and scenic rivers” based on their free-flowing condition and outstanding scenic, recreational, wildlife, cultural, and historic values.

Retaining the natural beauty and rural character of the SuAsCo Watershed is challenged by growth and development, as this area is one of the most rapidly growing in Massachusetts and, as such, is facing severe resource challenges. Rapid growth and development have placed land prices at a premium, making open space and habitat protection ever more difficult. Many stretches of the Sudbury, Assabet, and Concord Rivers routinely fail their water quality standard for nutrient enrichment and experience both severe flooding and low flow concerns.  Water shortages are evidenced as many towns post water bans during the summer. The rivers’ assimilative capacity to handle nutrients is severely stressed by non-point sources (stormwater) and wastewater treatment plant discharges. Throughout much of the Sudbury River downstream into the Concord River, fish consumption is banned due to mercury-laden sediments from the Nyanza Superfund Site. Invasive aquatic plant species compromise the river habitat for native species, and impair the recreational experience for boaters and anglers.



  • SuAsCo Watershed
  • Community Council
  • Suite 200
  • 118 Great Road
  • Stow, MA 01775
  • 978-461-0735

  • (c) 2012
  • Site by Boston University CDIA
  • Christine, Rachel, Zoe