Do not believe in the legend of a beast suck Thang Hen Lake up in one night, Lung Tao village people have their own decipher of the mysterious phenomenon.
Follow the giant fish group's trails
Thang Hen Lake has been a natural fish source to feed the local people for hundreds of years, including the giant freshwater fish swarms moving in water up, water down days.
Mr. Thang childhood memories associated with parents' footsteps into the Thang Hen lake for setting fishing-tackles or raising the fishing net for tiny shrimp. If not had them all at a time, they switched them to salted source or dry preserved for winter. In bad weather, people of Lung Tao were to catch a quintal of tiny shrimp, serveral loads of shrimp a day. There were carps as long as arm length, fin as large as mouth of drinking cup, very spectacular. Those were not promptly withdrawn as the water drained off, catched by people could be weighed more than ten kilograms. In addition to carps, Thang Hen lake also has such fish as pimelode.. with enormous weight. In the meantime, Lung Tao villagers sent them to Cao Bang town, a dozen miles away, for sale.
The riddle is that Thang Hen Lake is drained off to the bottom, 6 months a year. The lake bed is just like a luxuriant grassy plain. Many people take advantage of the ground to increase crops. The phenomenon is explained that there are many caves at the bottom of the lake. Each cave mouth perimeter is almost a meter long. From these caves mouth too, when the water come back there are gushing water comlumns. Sometimes there must be dozens of water columns simultaneity erupt. When it is full, water reaches to the walking path which is 100m to the bottom. The water gets drained swiftly and so does it come back.