The Chinese sturgeon is at risk of extinction as the Yangtze River becomes more polluted and crowded, according to state media of China.

Researchers from the Chinese Academy of Fishery Sciences documented zero reproduction rates for the sturgeons in the Yangtze River in 2013, local media organization Xinhua reported. This is the first time there have been no signs of natural reproduction of the species since the scientists started monitoring the sturgeon population 32 years ago.

There were no young sturgeons swimming in the river during August, the time of the year when they are usually abundant. Furthermore, no eggs laid by the wild sturgeons were found in the river.

"No natural reproduction means that the sturgeons would not expand its population and without protection, they might risk extinction," investigator from the academy, Wei Qiwei, told Xinhua news agency on Saturday.

The International Union for the Conservation of Nature has included the sturgeon in their critically-endangered list, according to The Telegraph. Qiwei stated that only 100 sturgeons remain in the wild, as compared to thousands recorded in the 1980s. The Chinese sturgeon was believed to have existed for more than 140 million years, along with the dinosaurs.

Researchers linked the sudden population decline of the fish to the increasing pollution levels and the construction of the dams along the river. The Yangtze River is home to the world's largest dam, the Three Gorges. Environmental campaigners argued that the dams caused the degradation to the river's ecosystem and destroyed the natural habitats of many species.

"Wild animals must have a complete living environment and the dam has affected their living conditions. Their extinction was forecast when the dam was built," Xie Yan, a researcher at the Institute of Zoology at the Chinese Academy of Sciences, told the South China Morning Post.

Humans also contributed to the problem, as sturgeons are often killed by fishermen's nets and ship propellers.