The man was visiting the waterfall with his family on September 1 when his son slipped into the stream that afternoon.
He swam into the water to rescue the boy, who was helped safely ashore by local residents. The father, however, was swept away by the fast-flowing current and went missing.
His body was found by rescue teams at around 7 am on September 2 and later handed over to his family.
A representative of the Tien Nu Waterfall ecotourism site said it was the first fatality there since the attraction opened.
The site has rescue personnel and equipment as well as warning signs, but prolonged heavy rain in recent days had raised water levels and made currents much stronger than usual, the representative said.
The attraction has been closed for 10 days, from September 1 to 10, while safety measures are reviewed.
The management said the closure would allow it to reassess warning systems, rescue plans and safety conditions around the waterfall and streams.
Visitors to waterfalls, rivers and streams are advised to follow warning signs and instructions from site staff and rescuers, particularly during heavy rain when water levels and currents can change rapidly.
Tien Nu Waterfall, also known as Dang Mo Waterfall, is a ticketed ecotourism attraction in Thien Thuat Commune, about 90 km from central Lang Son and over 160 km from Hanoi.
Fed by two upstream waterfalls, the stream flows through a mountainous area surrounded by forest. A pool at the foot of the waterfall is known for its turquoise water, created as the flow passes through limestone formations.
The dry season from November to May is generally considered the most suitable time to visit, when conditions are more favourable for travel and outdoor activities.
