The Upper Passaic River in New Jersey is the section of the Passaic River above the Dundee Dam, including the Great Falls. The entire river flows for 81 miles from its river's source in Mendham to the river mouth at Newark Bay in the northeastern part of the state. The Passaic traverses 45 municipalities, and its watershed provides drinking water for more than 3.5 million people in the region. The midpoint of the upper river generally delineates the Passaic-Bergen, Passaic-Essex, Essex-Morris, Morris-Union and sections of the Morris-Somerset county lines.