The Carmans River is a 10-mile (16 km) long river in Brookhaven in Suffolk County on Long Island.
It is one of the four largest rivers on Long Island and is like the other Long Island rivers in that is totally groundwater generated (e.g., no lakes). Almost all of the river is specifically protected by the Central Long Island Pine Barrens. All of it is designated by New York State as either a "Scenic River" or a "Recreational River."
Adjoining the river is the Wertheim National Wildlife Refuge.