Tamil festival on the 18th day of Aadi month celebrating River Kaveri's abundance with offerings to the water.

Aadi Perukku, also called Pathinettam Perukku, falls on the eighteenth day of the Tamil month of Aadi and honours the rivers — above all the Cauvery — at the point in the monsoon when they run at their fullest. Perukku means rising or swelling. It is a festival of gratitude to water as the source of the harvest, and it is celebrated on the riverbanks: families gather at the ghats of the Cauvery, Vaigai, Tamiraparani and Bhavani, cook and eat together, and float lamps and offerings on the water. Newly married couples are honoured, and married women tie a fresh yellow thread. Unlike most of Aadi, which is inauspicious for new beginnings, Aadi Perukku is regarded as a favourable day for sowing and for domestic celebration.

No fast is kept. The day is a feast, traditionally eaten together on the riverbank.