The Jiangong Islet is a tidal island in Jincheng Township, Kinmen County, Fujian Province, Republic of China (Taiwan).
Jiangong Islet
Jiangong is connected to main Kinmen island by a causeway which only appears in low tide
A tidal island is a raised area of land within a waterbody, which is connected to the larger mainland by a natural isthmus or man-made causeway that is exposed at low tide and submerged at high tide, causing the land to switch between being a promontory/peninsula and an island depending on tidal conditions.
St Michael's Mount, Cornwall, at high tide, c. 1900
Cramond Island, Scotland, at high tide: the causeway is submerged, but the anti-boat pylons are still visible
Mont Saint-Michel in Normandy
Rough Island opposite Rockcliffe, Dumfries & Galloway, Scotland