Rattanai Reservoir is a small-scale irrigation project located in Khao Kho District, Phetchabun Province. It was constructed to manage water resources for agriculture and domestic use by communities in the highlands, which historically suffered from frequent water shortages during the dry season. According to tourism data and related agencies, the reservoir has a capacity of approximately 2.02 million cubic meters, covering an area of ​​about 1,600 rai (approximately 66 hectares). It features a spillway system and earthen dams to control water flow to surrounding agricultural areas.

Although its primary purpose is irrigation, its location in a valley surrounded by complex mountain ranges makes Rattanai Reservoir a key element contributing to the ideal environment for the formation of Khao Kho's sea of ​​mist. At night, the lower temperatures cause moisture from the water surface and surrounding forests to condense into mist that blankets the valley. Combined with the cool climate and altitude of Khao Kho, this creates a thick sea of ​​mist that is commonly seen in the early morning, especially during the rainy and winter seasons.

A significant charm of Rattanai Reservoir is that, at certain times of the morning, tourists can barely see the water below. The entire valley is covered in thick, soft white mist, like an ocean of clouds. Looking from the viewpoint on Highway 2196 or near the Khao Kho Post Office, you can see mountain ranges interspersed with a sea of ​​mist stretching as far as the eye can see. As the sun begins to shine through the mountaintops, the golden light gradually hits the layers of mist, creating a breathtaking landscape that has become one of the iconic images of Khao Kho and Phetchabun province tourism.

The atmosphere around the reservoir is tranquil, a stark contrast to the bustling tourist areas. Tourists can enjoy the cool breeze throughout the day and see the water's surface reflecting the surrounding mountains and pine forests. During the rainy and winter seasons, low-lying mist sometimes hovers above the water for almost the entire morning, making this area ideal for relaxation, photography, enjoying nature, or a leisurely scenic drive. Furthermore, Khao Kho's cooler temperature compared to the plains contributes to the reservoir's refreshing atmosphere year-round.

Rattanai Reservoir is also connected to other important tourist attractions in Khao Kho, including viewpoints showcasing the sea of ​​mist, cafes, resorts, and several campsites. In particular, the viewpoint near the Khao Kho Post Office is one of the most popular spots to see the sea of ​​mist, with many tourists arriving before sunrise during the peak tourist season from October to January. To witness the moment when the sea of ​​mist gradually changes color as the morning light shines over the valley, the beauty of the landscape, the cool air, and the ever-changing fog conditions make each visit to Rattanai Reservoir a unique and charming experience.

• From Phetchabun town center, take Route 21 north, then turn left onto Route 2258 heading up towards Khao Kho. Follow the signs toward the Khao Kho District Office. The reservoir is located in the valley below Route 2196. The drive takes about 1 hour and 15 minutes. Vehicles of all types can access the area, but drivers should be careful navigating the winding mountain roads.

• Arrive before 06:00 AM for the best chance to see dense sea of mist.

• Visit during the rainy season and winter for the most consistent fog conditions.

• Bring a light jacket because mornings on Khao Kho can be very cold.

• Check the weather forecast before traveling to improve mist-viewing chances.

Admission Fees:

• Free admission.

Opening Hours:

• Open daily from 06:00 AM – 06:00 PM (for the reservoir ground areas). Elevated roadside viewpoints are accessible 24 hours.