| Casnell Island | |
| Native Name: | Maori: Maunganui |
| Nickname: | --> |
| Coordinates: | -36.49°N 174.726°W |
| Location: | Auckland |
| Waterbody: | Mahurangi Harbour |
| Area M2: | 68000 |
| Length M: | 386 |
| Width M: | 230 |
| Elevation M: | 40 |
| Country: | New Zealand |
| Country Admin Divisions Title: | Auckland Region |
Casnell Island is an uninhabited island located in the Mahurangi Harbour, Auckland Region, New Zealand. Casnell Island is managed by the Department of Conservation.[1]
The island is located in the Mahurangi Harbour at the mouth of Te Kapa River. It is accessible from Scotts Landing at low tide via a causeway.[2] It is the largest island found in the Mahurangi Harbour.
The island is formed from Waitemata Group sandstone and mudstone.
Much of the island is dominated by kanuka forest, with areas of pōhutukawa, kōwhai and grassland.
The island was a pā site in the 16th century,[2] serving as a defensive fort at the entrance of the Mahurangi Harbour.[3]