Thang Hen Lake

Thang Hen is a group of connected lakes in a karst basin east of Cao Bang, sitting between limestone walls with forest on them, and their behaviour is the interesting part: they are fed and drained through underground channels in the rock, so the water level changes markedly through the year and at times some of the lakes empty almost completely, refilling when the system delivers again. The Tay name is usually given as the tail of a bee, from the shape. Rafts and boats run on the main lake when it is full. The site is part of the Non Nuoc Cao Bang geopark.

What you'll find

• Lakes connected underground - fed and drained through the rock.
• Levels that change sharply - some emptying almost completely.
• Limestone walls and forest - the basin around them.
• Rafts on the main lake - when there is water.

When to go

August to November, when the lakes are fullest. Half a day.

Things to know

In the dry months the lakes can be very low or dry, which is the main risk of the trip. Facilities are basic. Boats operate only when levels allow. The road in is winding.

Nearby

Cao Bang is west; Nguom Ngao and Ban Gioc are north-east.

Key facts