Amid the windswept seascape of Lý Sơn Island, the Thới Lới volcanic crater is not only a remarkable geological relic formed millions of years ago, but also home to the largest freshwater reservoir on the island—a lifeline for local agriculture and daily life.
The Thới Lới reservoir has a storage capacity of approximately 270,000 cubic meters, ingeniously constructed within the ancient volcanic crater itself. The project includes a dam standing 11 meters high with a crest length of 208 meters, making full use of the crater’s natural topography to collect and store rainwater—an effective solution to Lý Sơn’s long-standing freshwater scarcity.
Mount Thới Lới rises about 169 meters above sea level, making it the highest point and the largest volcano on Lý Sơn Island. The crater measures roughly 350 meters in diameter, while the volcano’s base stretches up to 1.4 kilometers wide. Inside the crater, steep inner walls and a deep central basin create ideal conditions for water storage. Beneath the surface lies a clay layer over 5 meters thick, which helps retain water and ensures the reservoir operates stably throughout the year.
Water from the Thới Lới reservoir flows down to regulating tanks at the foot of the mountain, then travels through a 300-millimeter pipeline system to irrigate local farmland. Currently, there are around 30 connection points, allowing residents to access an automatic irrigation system that operates entirely without pumps, thanks to the natural water pressure created by elevation differences. This system supplies water to nearly 60 hectares of agricultural land, primarily onion and garlic fields—the island’s signature crops—while significantly reducing production costs.
According to estimates, the Thới Lới crater can collect up to 700,000 cubic meters of rainwater annually. After accounting for evaporation and seepage, the reservoir’s designed capacity of 270,000 cubic meters is considered optimal, ensuring both efficiency and sustainability. As the first irrigation infrastructure project on Lý Sơn Island, it plays a vital role in securing livelihoods for the local community.
Beyond its practical importance, the Thới Lới reservoir has become a compelling destination for visitors. Located in An Hải Commune, the journey to the summit of Mount Thới Lới takes travelers past this expansive freshwater lake nestled inside the crater, resembling a giant natural funnel. This very crater once erupted with molten lava millions of years ago, shaping the distinctive volcanic landscape that defines Lý Sơn today.
The reservoir reveals a different beauty at each time of day. In the early morning, soft sunlight spreads across the water’s surface, creating a clear, turquoise hue that sparkles gently. The surroundings are calm and refreshing, accompanied only by birdsong and the whisper of the breeze.
By midday, under stronger sunlight, the lake deepens into a rich blue tone, reflecting the vast sky and drifting white clouds above. Although the heat intensifies, the cool color of the water brings a sense of relief and tranquility.
As evening falls, the reservoir darkens, becoming almost mirror-like. The scene grows quiet and contemplative, with only the sound of wind and distant ocean waves. In the fading light, the Thới Lới reservoir seems to drift into rest, awaiting the dawn of another day.
Today, the volcanic crater reservoir of Thới Lới stands not only as the lifeblood of Lý Sơn Island, but also as a unique attraction—where visitors can admire rare natural scenery while gaining insight into how humans have wisely adapted to and harnessed the gifts of nature. A visit to Lý Sơn would be incomplete without experiencing this extraordinary landscape.
