China’s Three Gorges Dam on the Yangtze River is the world’s largest hydroelectric power station in the world by installed capacity (22,500 MW). The dam is about 2.3 km long and 185 m high. It creates a reservoir nearly 600 km long, stretching upriver behind the dam. When the reservoir filled, it held over 39 trillion kg of water. That’s so much mass that it slightly altered Earth’s rotation and shortened the length of a day by about 0.06 microseconds. It also shifted the Earth’s axis by around 2 cm.