Baiji

The baiji was a pale blue-grey river dolphin with a long narrow beak, small eyes and broad rounded flippers. Females were larger than males, and adults measured approximately 1.4–2.5m. It was native only to China's Yangtze River system. (Wikipedia, general species account)

Baijis inhabited large river channels and connected lakes and used echolocation to navigate turbid water and locate freshwater fish. They generally travelled alone or in small groups and surfaced with a low, rolling motion. The last universally accepted records date from the early 2000s; later surveys have not produced confirmed evidence of survival. (Wikipedia, general species account)