The Auckland isthmus, also known as the Tāmaki isthmus, is a narrow stretch of land on the North Island of New Zealand in the Auckland Region, and the location of the central suburbs of the city of Auckland, including the CBD. The isthmus is located between two rias (drowned river valleys), the Waitematā Harbour to the north, which opens to the Hauraki Gulf / Tīkapa Moana and Pacific Ocean, and the Manukau Harbour to the south, which opens to the Tasman Sea. The isthmus is the most southern section of the Northland Peninsula.