The Tar Slick is a naturally-spawning object exclusive to the Shipwrecked DLC. It can be found anywhere in the Medium Ocean or Deep Ocean. It is a source of Tar, which must be extracted by building a Tar Extractor. A Tar Slick does not run out, and cannot be destroyed, making Tar a renewable resource. A Tar Slick can also be created at the player's will using a Quacken Drill, thus making Tar Slick renewable.
The Tar Slick was added to the Shipwrecked DLC more than a year after its official completion in the Home Sea Home update, after being tested in a beta branch for several months.