Chinese river dolphin

The Chinese river dolphin ("Lipotes vexillifer") or baiji was a river dolphin. It was found only in the Yangtze River in China. The last confirmed sighting of the baiji was in 2004 but there were possible sightings in 2007 and 2016 as well. The baiji was declared functionally extinct in 2007. that means experts said that even if there had been a few baiji left alive in 2007, there were probably not enough left to have young and keep the species alive. The IUCN Red List says the baiji is critically endangered but not really extinct.
Description.
The baiji was a graceful animal, with a long, narrow and slightly upturned beak and a flexible neck. As opposed to some other freshwater dolphins, like the Indus River dolphin, its eyes were functional, although greatly reduced. Its coloration was bluish-gray to gray above and white to ashy-white below. It weighed 135 – 230 kg (300 - 510 lb) and measured as much as 2.5 m (8.2') in length.
Reasons for extinction.
The World Conservation Union (IUCN) noted these threats to the species: 
Further studies have noted the environmental impact of building the Three Gorges Dam on the living space of the baiji.
It was the first dolphin species that humans have made extinct.