Tran Thoi, from Cam Kim commune in Hoi An city, found the turtle, which is 43cm in length and 7.6kg in weight, in his net, while fishing on the Thu Bon river.
He handed over the animal to the management board on January 30.
Known as the olive ridley sea turtle (scientifically called Lepidochelys olivacea), the turtle is included on the red book of threatened species by the International Union for the Conservation of Nature, indicating it is an endangered species.
Confirmed to be in a good health, it was released from Cua Dai beach the next day.
Encountering a sea turtle in the river mouth area is very rare. The animal may have gotten lost while foraging for food.
In recent years, the board has worked to increase public awareness of sea turtle conservation and develop a voluntary network for prompt reports of trapped turtles.
In the past two years, approximately 1,400 baby turtles have been hatched along the beaches of the Cham Islands. The eggs were brought from Con Dao Island, believed to be the largest nesting site for sea turtles in the country.
The Cham Islands, 20km off the coast of Hoi An city, are home to 1,500ha of tropical forests and 6,700ha of sea featuring a wide range of marine fauna and flora, including many endangered species. It also houses 1.26sq.km of coral reefs.