A watershed is an area that all drains to a common point. Its boundaries are determined by ridges or high points known as watershed divides. Rain falling mere inches apart on opposite sides of a ridge or watershed divide may ultimately take very different paths to the ocean. For instance, some rain that falls in Florida, MA flows down the Cold River to the Deerfield River to the Connecticut River to Long Island Sound. BUT, just to the west, rain will land on the other side of the ridge, flow down the Hoosic River to the Hudson to New York Harbor, hundreds of miles away.
The great thing about doing conservation on the watershed scale, rather than by town, county or other municipal boundary, is that we can have a real impact on water quality because we are focused on the entire area that contributes water to our river. The quality of water in the river is a direct reflection of the watershed that provides its runoff and groundwater to the river.
In the map below, you can see all the major tributaries to the Deerfield River traced in red. Notice that about half of the watershed is located in Vermont, and the other half is in Massachusetts. The green line that wiggles down the left half of the map shows the major watershed divide between the Connecticut River (to which the Deerfield drains) and the Hudson River, whose basin lies just to the west of ours. This map was created using the National Atlas, here: http://nationalatlas.gov/streamer/Streamer/streamer.html
On our hydrology page, you can view a detailed map of our entire watershed with all of its tributaries, roads and towns.