This is some info on the Baiji from wikipedia.
The Baiji population declined drastically in recent decades as China industrialized and made heavy use of the river for fishing, transportation, and hydroelectricity. Efforts were made to conserve the species, but a late 2006 expedition failed to find any Baiji in the river. Organizers declared the Baiji "functionally extinct", which would make it the first aquatic mammal species to become extinct since the demise of the Japanese Sea Lion and the Caribbean Monk Seal in the 1950s. It would also be the first recorded extinction of a well-studied cetacean species (it is unclear if some previously extinct varieties were species or subspecies) to be directly attributable to human influence.
In August 2007, Zeng Yujiang reportedly videotaped a large white animal swimming in the Yangtze. Although Wang Kexiong of the Institute of Hydrobiology of the Chinese Academy of Sciences has tentatively confirmed  that the animal on the video is probably a baiji, the presence of only one or a few animals, particularly of advanced age, is not enough to save a functionally extinct species from true extinction. The last known living baiji was Qi Qi (淇淇) who died in 2002.
Baiji are thought to breed in the first half of the year, the peak calving season being from February to April. A 30% pregnancy rate was observed. Gestation lasts 10-11 months, delivering one calf at a time; the interbirth interval is 2 years. Calves measure around 80-90 centimetres (32-35 in) at birth, and nursed for 8-20 months. Males reach sexual maturity at age four, females at age six. Mature males were about 2.3 metres (7.5 ft) long, females 2.5 metres (8 ft), the longest specimen 2.7 metres. The animal weighed 135-230 kilograms (300-510 lb), with a lifespan estimated at 24 years in the wild.
When escaping from danger, the Baiji can reach 60 km/h (37 mph), but usually stays within 10 to 15 km/h (6-9 mph). Because of its poor vision and hearing, the Baiji relies mainly on sonar for navigation.
Historically the Baiji occurred along 1,700 kilometres (1,000 miles) of the middle and lower reaches of the Yangtze from Yichang in the west to the mouth of the river, near to Shanghai. This had been reduced by several hundred kilometres both upstream and downstream, and was limited to the main channel of the Yangtze, principally the middle reaches between the two large tributary lakes, Dongting and Poyang. Approximately 12% of the world’s human population lives and works within the Yangtze River catchment area, putting pressure on the river. The construction of the Three Gorges Dam, along with other smaller damming projects, also led to habitat loss.
In the 1950s, the population was estimated at 6,000 animals, but declined rapidly over the subsequent five decades. Only a few hundred were left by 1970. Then the number dropped down to 400 by the 1980s and then to 13 in 1997 when a full-fledged search was conducted. Now the most endangered cetacean in the world, according to the Guinness Book of World Records, the Baiji was last sighted in August 2007. It is listed as an endangered species by the U.S. government under the Endangered Species Act.
The World Conservation Union (IUCN) has noted the following as threats to the species: a period of hunting by humans during the Great Leap Forward, entanglement in fishing gear, the illegal practice of electric fishing, collisions with boats and ships, habitat loss, and pollution. During the Great Leap Forward, when traditional veneration of the Baiji was denounced, it was hunted for its flesh and skin, and quickly became scarce.
As China developed economically, pressure on the river dolphin grew significantly. Industrial and residential waste flowed into the Yangtze. The riverbed was dredged and reinforced with concrete in many locations. Ship traffic multiplied, boats grew in size, and fishermen employed wider and more lethal nets. Noise pollution caused the nearly blind animal to collide with propellers. Stocks of the dolphin's prey declined drastically in recent decades as well, with some fish populations declining to one thousandth of their pre-industrial levels.
In the 1970s and 1980s, an estimated half of Baiji deaths were attributed to entanglement in fishing gear. By the early 2000s, electric fishing was considered "the most important and immediate direct threat to the Baiji's survival." Though outlawed, this fishing technique is widely practiced throughout China. The building of the Three Gorges Dam further reduced the dolphin's habitat and facilitated an increase in ship traffic.