The baiji, a freshwater dolphin known as the “goddess of the Yangtze” is extinct, scientists said this week. The latest search of the river produced no sightings of the species, which lived in the Yangtze for 20 million years. The demise is blamed on overfishing, and the construction of the Three Rivers Dam, the largest hydroelectric river dam in the world, and 5 times the size of the Hoover.