The Saritphong Dam (also called Phra Ruang Dam) is the oldest large hydraulic work in Thailand, built in the late 13th century to gather monsoon runoff from the Khao Phra Bat Yai hills and feed it through canals into the moats and ponds of Sukhothai. The dam is an earthen embankment about 400 metres long and 10 metres high, plugging a narrow gap between two hills about 4 km southwest of the central park.
The dam is still in use, refurbished and integrated into the modern irrigation system, and the reservoir behind it is now a quiet recreation area with a few stalls selling cold drinks. The site is rarely visited by foreign tourists but is part of the engineering reason Sukhothai could exist where it did. A short paved road runs up onto the embankment with views back across the plain.