An internally mounted rowboat rowing fin system that includes two rotating fin assemblies mounted on the inside surface of the watercraft's opposite sidewalls. Each fin assembly includes a rotating vertical post held on the inside surface of the sidewall by a mounting tube selectively mounted or integrally formed on the sidewall. Longitudinally aligned and disposed inside each mounting tube is a hollow, elongated sleeve. Disposed inside each elongated sleeve is a rotating post that extends upward above the gunwale and into the water below the elongated sleeve. A pivoting fin arm with a flexible fin attached thereto is pivotally attached to the lower end of each rotating post. Attached to the upper end of each rotating post is a perpendicularly aligned handle bracket. A rowing handle is pivotally attached at one end to the handle hinge. During use, the two handles extend inward from the sidewall and are grasped by the rower. Both handles are able to swing in a vertical 180 arc over their respective handle hinges thereby allowing the fins to rotate 180 and sweep in opposite directions.