R.I. Gen. Laws § 42-3-6: Jurisdiction over waters.

The jurisdiction of counties separated by, or bordering on, the public waters within the jurisdiction of the state, shall be concurrent over those waters, except as is hereinafter provided. The waters of Narragansett Bay, and the lands and rocks therein, situated to the northward of a line drawn from the mouth of Pawtuxet River to Sabin’s Point, shall be deemed a part of the county of Providence, and be within the jurisdiction of Providence County; and all the other waters of Narragansett Bay shall not be deemed to make a part of or be within the sole jurisdiction of any one particular county.