The Kallada river, which originates near Ponmudi from the Kulathupuzha hills Western Ghats in Thiruvananthapuram District, is formed by the confluence of three rivers, viz., Kulathupuzha, Chenthurnipuzha, and Kalthuruthipuzha, and after traversing a distance of about 121 km (75 mi) through virgin forests finally debouches into the Ashtamudi wetland at Neendakara (a fishing harbour) near Kollam as it enters the Lakshadweep Sea, part of the Arabian Sea.
Its upper portion is crossed by the Sohan torrent, while the Sutlej sweeps into its lower end through a break in the hills, and flows in a southerly direction until it turns the flank of the central range, and debouches westwards upon the plains.