Lake Hopatcong is the largest freshwater body in New Jersey, United States, about 4 square miles (10 km²) in area. Located 30 miles from the Delaware River and 40 miles from New York City, the lake forms part of the border between Sussex and Morris counties in the state's northern highlands region. Lake Hopatcong was produced by damming and flooding of two ponds, known as the Great Pond and Little Pond, and the Musconetcong River, its natural outlet.