The Paulins Kill (also known as Paulinskill River) is a tributary of the Delaware River in northwestern New Jersey in the United States. With a long-term median flow rate of 76 cubic feet of water per second (2.15 m³/s), it is New Jersey's third-largest contributor to the Delaware River, behind the Musconetcong River and Maurice River. The river drains an area of across portions of Sussex and Warren counties and 11 municipalities. It flows north from its source near Newton, and then turns southwest. The river sits in the Ridge and Valley geophysical province. The Paulins Kill was a conduit for the emigration of Palatine Germans who settled in northwestern New Jersey and northeastern Pennsylvania during the colonial period and the American Revolution. Remnants of their chiefly agricultural settlements are still found in local architecture, cemeteries, farms and mills, and the area remains largely rural. Flowing through rural sections of Sussex and Warren counties, it is regarded as an excellent place for fly fishing. The surrounding area is used for hiking and other forms of recreation such as observing birds and other wildlife. Course The main branch of the Paulins Kill begins to form immediately north of Newton, in the marshes that straddle the town. The headwaters start near Route 622 in Fredon Township. It flows southwest for the rest of its journey, through Hampton and Stillwater townships in Sussex County. Trout Brook, which rises on Kittatinny Mountain, flows into the river near Middleville in Stillwater Township. Swartswood Lake feeds Trout Brook through Keen's Mill Brook. The Paulins Kill continues its course southwest, entering Warren County, where it initially forms the border between Frelinghuysen and Hardwick townships. It enters Blairstown immediately after, where it is joined by Blair Creek, named (as is the town) for John Insley Blair (1802–1899), as well as Jacksonburg Creek, Susquehanna Creek, Dilts Creek and Walnut Creek. Yards Creek, which rises at the Yards Creek reservoir in Blairstown, enters the Paulins Kill near the hamlet of Hainesburg in Knowlton Township. Finally, in Warren County its waters enter the Delaware River just south of the Delaware Water Gap at the hamlet of Columbia in Knowlton Township. After the establishment of Swartswood State Park in 1914, a dam was built in the 1920s across the river in Stillwater Township to create Paulinskill Lake. Summer cottages were built to attract vacationers from nearby New York City. Today, the lake