Lopatcong Creek is a 12.0-mile-long (19.3 km)[1] tributary of the Delaware River in Warren County, New Jersey in the United States.

[2] The source of the stream is Scotts Mountain in Harmony Township.

[3] It was one of the chief water sources for the Morris Canal, in particular from Inclined Plane 9 West in Port Warren to Lock 10 West in the Green's Bridge section of Phillipsburg.

[4][5] The Lopatcong joins the Delaware in Phillipsburg.

The name of the creek is derived from the Lenni Lenape — Lowan peek achtu onk, which meant "winter watering place for deer,"[6][7] or "at the swift river".