Which Indian festival features the traditional snake boat race, popularly known as Vallam Kali?

Explanation

Onam. The snake boat race, popularly called Vallam Kali, is a highlight of the Onam festival in Kerala. Onam, a harvest festival celebrated in August–September (Chingam month), also features Pookalam (flower carpets), traditional dances like Thiruvathira, and grand feasts (Onasadya).