Dangzhuo Bay

Off Hainan's northwest coast, Dānzhōu Bay opens towards the Gulf of Tonkin. At Yángpǔ on its shore, salt workers developed a method of filtering seawater through dried sand and evaporating the brine in shallow basalt basins. The salt fields date back to the Song. Farther offshore, waves in the gulf change with the monsoon, generally approaching from the northeast in winter and from the south in summer.