The Dorn, from the gaelic word narrow channel, refers to the channel which connects several sheltered bays to the lough. Its an extensive area of mud-flats, sheltered bays, pladdies and seabed on the eastern side of Strangford Lough. At the northern end of the reserve, Gransha Point, a spit of shingle and bedrock, extends over 1km into the Lough.
Near the mouth, rock barriers or sills hold back water as the tide falls, creating saltwater rapids, a feature which is unique in Ireland. These conditions allow extraordinary growth of marine plants and animals.
Unusually large sponges, anemones and sea squirts are abundant. Starfish, sunstars and brittle stars are among the many deeper water animals able to survive in shallower areas here. Within the maze of sheltered bays near Bishop's Mill, fine areas of saltmarsh with glasswort and sea purslane can be easily viewed from the road. The foreshore supports large numbers of wintering wildfowl and waders including curlew, goldeneye and red-breasted mergansers. Brent geese, shelduck and teal are frequent and may be seen from high points along the road north of Ardkeen. Feral Canada geese occur in the summer. Common seals frequently bask on the rocks below Castle Hill and may be seen with pups on nearby pladdies in July. (source DOE NI)