Long strands of river weed grow in flowing Lao rivers. In Luang Namtha province they are collected by the locals and served up either as a thick, simmered, spicy sauce or dried in thin sheets which have been sprinkled with tamarind and ginger juice and other aromatics such as sesame seeds, tomato and garlic. The dry sheets are cut into small squares and flash shallow fried for a tasty drinks snack. Kai paen can also be toasted over a fire or in a microwave oven.
Here is the process of collecting and preparing river weed for comsumption and sale in Luang Prabang, shared by Joost Foppes via Facebook. Thanks, Joost!