The Kollidam referred as Coleroon is a river in southeastern India. The Kollidam is the northern distributary of the Kaveri River as it flows through the delta of Thanjavur. It splits from the main branch of the Kaveri River at the island of Srirangam and flows eastward into the Bay of Bengal.
The river Kaveri splits into four streams known as Kollidam Aru, Kaveri, Vennaru and Puthuaru. The purpose of the Kallanai was to divert the waters of the Kaveri across the fertile delta region for irrigation via canals and to its northern delta branch Kollidam.