The Hukou Waterfall, the largest waterfall on the Yellow River, the second largest waterfall in China, is located at the intersection of Shanxi Province and Shaanxi Province. The Hukou Waterfall is naturally formed when water of middle reaches of the Yellow River flows through Jinxia Grand Canyon. The width of the waterfall changes with the season, usually 30 meters wide but increasing to 50 meters during flood season. It has a fall of over 20 meters. When the Yellow River surges towards the Hukou Mountain, blocked by mountains on both sides, its width is abruptly narrowed down to 20-30 meters. The water speeds up with increasing water power. Then it rushes down from the narrow mouth, forming a grand waterfall of 15 meters high and 20 meters wide, as if water is pouring down from a huge teapot. Hence it gets the name Hukou (Flask Mouth) Waterfall.