Marpi Reef or Marpi Bank is a narrow seamount lies north of Saipan. With length of and in width, the reef is generally similar to the Tatsumi Reef south of Tinian in terms of orientation in a northeast to southwest. The peak of the seamount is at 26 fathoms or 53 m under water surfaces.
It is one of fishing points in the region, and various cetaceans (whales and dolphins) migrate and live in the waters including humpback whales.