The Manumuskin River is a 16.3-mile-long (26.2 km) tributary of the Maurice River in Cumberland County, New Jersey in the United States. The Manumuskin River flows through a relatively pristine forested area in the southern Pine Barrens of Cumberland County, as well as Atlantic white cedar bogs and salt marshes in its lower reaches. The name is of Lenape origin. A local nonprofit organization, Citizens United to Protect the Maurice River and Its Tributaries, Inc., is a regional watershed organization that focuses its work on the Maurice River watershed, which includes the Manumuskin.