The new regulation was issued following consultation and approval from Ha Giang Tourism Promotion Centre.

The move came after videos of a female visitor wearing a bikini while touring the river recently went viral.

Speaking about the new regulation, deputy director of the Ha Giang Tourism Promotion Centre, Vu Thi Mai Huong, said that the Nho Que River lies in the Tu San Canyon which is not only a tourist site but also a geographical heritage. So it is necessary to protect its images and enhance its values.

"In the old regulations issued in 2018 by the Ha Giang Provincial People's Committee, we also asked visitors to wear suitable clothes when visiting local tourist sites," the official said. "We don't operate swimming activities in the Nho Que River so it's unsuitable for visitors to wear bikinis here."

The official added that tourists are encouraged to wear local traditional costumes when visiting the river and dining and smoking are also banned on boats.

With a depth of about 800m, a length of 1.70 km and a cliff slope of 70-90o, Tu San is believed to be the deepest canyon in Southeast Asia.