Flowing along the western branch of the Ho Chi Minh Trail, the Chay winds through Phong Nha - Ke Bang National Park in Quang Binh Province. Its waters and karst landscape have turned it into a popular eco-tourism attraction, especially among western tourists coming in summer.
The Phong Nha - Ke Bang Tourism Center offers water-based activities to visitors, including river swimming, kayaking and visits to the Dark Cave.
According to the center, aside from swimming, one of the most exciting activities for tourists is ziplining across the Chay River.
Floating pontoons are set up by the tourism operators. Many visitors choose to leap from the pontoons into the water.
Another visitor and her daughter opt for a kayak ride, taking in the views at the natural heritage site.
Among the more thrilling experiences is jumping into the river from a bamboo bridge.
David Hall, 23, from the U.K. said he was thrilled at trying the zipline ride over the river. From up high, he and his girlfriend could take in the limestone scenery surrounding them, he said.
"It was amazing to swim in such emerald-green water. Our favorite part was definitely the zipline across the river."
Tourists have fun with water activities on the Chay River. Video by VnExpress/Vo Thanh