Kallanai Dam, Water heritage site and ancient dam in Thanjavur district, India.

Kallanai Dam is a barrage of unhewn stone across the Kaveri in Thanjavur district, 329 m long, 20 m wide and 5.4 m high. Its crest carries a bridge deck with a railing and lamp posts, and the river splits into four streams below it.

Karikala Chola ordered the construction in the second century to improve irrigation in the Kaveri delta region. British engineers made adjustments in the 19th century by raising the height and adding additional sluices.

The name Kallanai means "stone dam" in Tamil, from kal (stone) and anai (dam), referring to the unhewn blocks laid across the Kaveri. Delta farmers have petitioned the Tamil Nadu government to honour Karikala Cholan, the Chola king credited with building it. During irrigation seasons water is released into the Kaveri, Vennaru and Puthu Aru, and during floods diverted to the Kollidam.

Access to the dam is possible year-round, though cooler months provide a more comfortable visit. Visitors can walk along the wide dam crest and observe the river branches from above.

The construction works without moving parts or mechanical components, regulating water flow solely through its shape. Engineers worldwide still study the design today as an example of sustainable water management.