During low tide, people head onto the exposed mudflats carrying scoops and buckets to dig for the shellfish, which live beneath layers of sand and mud in brackish water.
After dark, many return with torches, racing against the incoming tide. Dotted with flickering lights, the riverbank becomes a busy scene as residents search for what locals often describe as a gift from nature.
Do Thi Kim, 58, said experienced harvesters could collect five to six kilogrammes of shellfish during a single outing at the start of the season.
The shellfish sell for around VND 30,000 (USD 1.15) per kilogramme in the shell and up to VND100,000 after being cleaned and prepared. They are commonly used in local dishes, including soups, porridge and egg-based meals.
For Ho Dinh Ngai, 65, the seasonal harvest is less about income than supplementing family meals. "Many people collect them to eat and sell, but at my age, having enough food for the family is already a joy," he added.
For many riverside households, shellfish harvesting provides an important source of additional income during quieter periods of the farming season. Others see it as a way to improve daily meals while introducing younger generations to local traditions.
Tran Thi My Ngoc, 44, recently brought her son, who had just completed Year 11, to the riverbank to experience the activity firsthand. She said the outing not only helped provide food for the family but also gave her son a better understanding of the hard work involved in making a living from the river.
Many local teachers and parents have also taken their children to the sandbanks during the summer holiday to experience shellfish harvesting and learn more about life in riverside communities.
As night falls, torchlights continue to flicker across the riverbank as residents follow the tide in search of the seasonal shellfish.