Phan Van Thai, 49, and his wife were fishing on the Co Chien River in Cho Lach District when they heard a loud splashing sound. On further inspection, they discovered a creature they could not identify trapped in their net.

"I’ve been fishing for the last 20 years, but I have never seen any fish as big and strange as this one," Thai said. The creature was approximately 2.3 meters (7.5 feet) long and weighed 150 kilograms (330 pounds).

The animal was dead, and Thai stored it in ice and waited for authorities to identify it. It was later identified as an Irrawaddy dolphin, a species of dolphin previously thought to have disappeared from Vietnam's Mekong River, Vu Long, director of the Center for Biodiversity Conservation and Endangered Species, told the media.

"In the last 30 years scientists have not recorded an Irrawaddy dolphin in Vietnam. I believe that the discovery of this dolphin species in the Co Chien River is an important, ground-breaking discovery that necessitates a research project."

The dolphin was an old female which had lost all her teeth, he added.

DNA samples of the dolphin were taken and its discovery was reported to the Directorate of Fisheries and the Department for Nature Conservation and Biodiversity.

The Irrawaddy dolphin (Orcaella brevirostris) is an euryhaline species of oceanic dolphin that lives in brackish water near coasts, river mouths and in estuaries, including the Mekong area in Southeast Asia.  It is protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora.

Some populations in Laos, Cambodia, Indonesia, Myanmar, the Philippines, Thailand and Vietnam are classified by the International Union for Conservation of Nature as critically endangered. A World Wildlife Fund repesentative told Thanh Nien that the species had been thought to be extinct in Vietnam and Laos.

A person violating regulations on management and protection of endangered or rare animal species in Vietnam could be fined between VND500 million ($21,400) and VND2 billion ($85,800) and imprisoned for one to 15 years.