| Nandalar | |
| Name Other: | Nandalaru |
| Subdivision Type1: | Country |
| Subdivision Name1: | India |
| Subdivision Type2: | State |
| Subdivision Name2: | Tamil Nadu |
| Subdivision Type3: | Region |
| Subdivision Name3: | South India |
| Subdivision Type4: | Origin |
| Subdivision Name4: | Kumbakonam, Tamil Nadu |
| Length: | 60km (40miles) |
| Source1 Location: | Kumbakonam |
| Source1 Coordinates: | 10.9709°N 79.3851°W |
| Source1 Elevation: | 20m (70feet) |
| Mouth: | Bay of Bengal |
| Mouth Location: | Tharangambadi, Mayiladuthurai, Tamil Nadu, India |
| Mouth Coordinates: | 11.0186°N 79.8556°W |
| Mouth Elevation: | 0m (00feet) |
Nandalar (நண்டலாறு) is a branch river of Cauvery River and flowing between Tiruvarur district and Mayiladuthurai district of the Indian state of Tamil Nadu. It act as a border line for Thiruvarur and Mayiladuthurai Districts.
Nandalaru => Nandu(Crab)+Kal(Rock)+Aaru Crab's Fossil in Rock found in this river. So this river got the name as Nandalaru.
Nandalar is a branch of River Cauvery.Nandalar river split from Cauvery near Kumbakonam and it flown through Kumbakonam, Komal, Avazhikkarai, Nallaathur. It drained in Bay of Bengal between Chandrapadi and Tharangambadi.[1]