The baiji occupied its own family, Lipotidae, a lineage separate from marine dolphins for over twenty million years. Its eyes were reduced almost to uselessness in the sediment-heavy Yangtze, and it located prey by echolocation. Estimates put the population at around six thousand in the 1950s.
The decline was incidental rather than targeted. Rolling hook longlines and electric fishing killed dolphins caught in the gear, heavy vessel traffic caused ship strikes and filled the river with noise that interfered with echolocation, and dam construction fragmented the habitat and altered flow. No hunt was ever mounted for the animal itself.
An intensive international survey in November and December 2006, using visual observers and acoustic detection over the full historic range, recorded no baiji. The species is generally described as functionally extinct, meaning any survivors would be too few to sustain a population. The IUCN still lists it as Critically Endangered rather than Extinct, because absolute proof of absence is difficult in a river of that size. An unverified sighting was reported in 2016.