The Watershed Institute

The Watershed Institute, formerly known as the Stony-Brook Millstone Watershed Association, is a New Jersey nonprofit organization devoted to promoting and protecting the watersheds of central New Jersey's Stony Brook and Millstone River, along with associated natural resources and beauty. Claiming to be central New Jersey's first environmental group, it was established in 1949. The organization promotes and advocates conservation and restoration of natural habitats, collects data on environmental conditions in its watersheds, and provides environmental education through numerous programs.

The organization is centered on its 950-acre nature reserve in Hopewell Township, Mercer County, which includes portions of Stony Brook, Wargo pond, over ten miles of trails, the seasonal Kate Gorrie Butterfly House, and the LEED-platinum Watershed Center for Environmental Advocacy, Science, and Education.