It would be unfair to compare Thac Ba and its lake, 170 kilometres northwest of Hanoi, to Ha Long Bay -- although some do -- but its beauty is jaw dropping and we'd highly recommend a stop if you're making your own way to Sapa or keen on exploring off the usual tourist trail.
The lake and its surrounds is considered an area of ecological and cultural importance. The region is home to a number of ethnic minority groups, most notably the Dao but also Tay, Nung, Thai, Muong, Giay and others, with many living along the banks of the lake and earning a living from its waters.
The area also has historical significance: in 1285 the Thu Vat Battle took place against Mongolian invaders and during the Vietnam/American war Thuy Tien cave was the base of Yen Bai provincial committee.
The lake was created when the Thac Ba Hydropower Plant was constructed on the Chay River in Yen Binh district. It is immense: more than 23,000 hectares, 80 kilometres long, up to 10 kilometres wide and 42 metres down at its deepest point. The landscape is stunning, with 1,331 islands, mostly covered in forest, and still, clear water.