The Hukou Waterfalls of the Yellow River is the only Yellow Waterfall on earth. The river narrows and cascades dramatically into a stone pond more than 30 meters below, creating the famous Hukou Waterfalls. The gentle water turbulent and gains speed as it rushed forward till it finally cascades over the waterfall, forming an illusion of water being poured from a kettle, hence its name "Hukou or Kettle spout". Like thousands of tumbling dragons or enraged animals that have just been set free, the yellow water plunged down, the pounding against the stones echoes like thunder. The most dramatic changes occur during deep winter and early spring when the river surface becomes frozen. Sometimes, the subsidiary falls freeze into icicles, creating images of crouching beast on top of the cliffs.