The Nandalar River is a river flowing between Tiruvarur district and Nagappattinam district of the Indian state of Tamil Nadu. It act as a border line for Thiruvarur and Nagappattinam Districts. Nandalar is a branch of River Cauvery. Nandalar river split from Cauvery near Kumbakonam.It drained in Bay of Bengal between Chandrapadi and Tharangambadi.