What Is A Watershed?

A watershed is an area of land that drains into a particular body of water, such as a stream, river, pond, or lake. A watershed is not determined by political boundaries, but instead is shaped by nature’s hills and valleys.

In New Jersey, we recognize 20 “watershed management areas,” which range in size from 165-square-miles to 885-square-miles.

The Watershed Institute focuses its work in the Millstone Watershed and the adjacent portion of the Central Delaware Watershed. We help other organizations around New Jersey care for the watersheds near them and advocate for state laws and policies to protect all of New Jersey’s watersheds.

Watersheds are like nesting Russian dolls. Small watersheds around the smallest streams fit within larger watersheds around the large rivers that they feed. For example, Harry’s Brook Watershed in Princeton is part of the Millstone Watershed, which is part of the Raritan River Watershed.

The Millstone Watershed is a 265-square-mile area that spans 25 towns across Mercer, Monmouth, Hunterdon, Middlesex, and Somerset counties. The Stony Brook is the largest of more than a dozen tributaries that flow into the Millstone River. This  38-mile river flows generally south to north until it joins the Raritan River, which empties into Raritan Bay near Sandy Hook, NJ. Other water bodies within the Millstone Watershed include Lake Carnegie, Peddie Lake, Beden Brook and Six Mile Run.

Within the Central Delaware Watershed, a 272-square-mile region located primarily in Hunterdon and Mercer Counties, are located the Assunpink Creek, Jacobs Creek, Shabakunk Creek and Mercer Lake.

The D&R Canal conveys water from the Delaware River across the Millstone Watershed to the Raritan River.