The Yinyang Sea (陰陽海) at the Northeast coast of Taiwan gained its name from the dual-tone colour of the water at the bay. This phenomena is due to the iron hydroxide-rich stream water which is yellowish-brown running into the bay, in contrast with the blue water towards the open sea.
Many people think that this is some kind of pollution but it is just pure act of nature, as the geological formation around this region is iron pyrite-rich rocks. When rainwater leaches the iron ions out of these rocks, the stream water becomes yellowish-brown.
