Canvey Island the 30 hectares known as West Canvey marshes, acquired by the RSPB in 2007, and the Canvey Wick nature reserve. Canvey Wick is a designated Site of Special Scientific Interest (SSSI) at the site of the abandoned and incomplete oil refinery. The foundations of the 100 hectare (0.4 sq mile) site were prepared in the 1970s by laying thousands of tonnes of silt dredged from the Thames; the abandoned and undisturbed area has flourished as a haven for around 1,300 species of wildlife, many of which are endangered or were thought to be extinct; including the shrill carder bee, the
Yalu River its length. Most of the river freezes during winter and can be crossed on foot. The depth of the Yalu River varies from some of the more shallow parts on the eastern side in Hyesan (1 m) to the deeper parts of the river near the Yellow Sea (2.5 m). The estuary is the site of the Amrok River estuary Important Bird Area, identified as such by BirdLife International. About 205 islands are on the Yalu. A 1962 border treaty between North Korea and China split the islands according to which ethnic group was living on each island. North Korea