The average annual runoff from the river system into the estuary is reported to be 76 cubic kilometers of freshwater.
The basin drainage area is 1,700 km² (660 mi²) and with an average annual rainfall of 2400 mm (94 in) it discharges 3.375 km³ (2,740,000 ac·ft) of flow annually.
It acts as a flood storage lake thus protecting the thickly populated city of Quilon (Kollam) and the coastal land.
The Kallada dam built across the Kallada river is 85.3 m high by 35 m long (280 ft by 115 ft) with a reservoir area of 23 km² (8.9 mi²) with a storage volume of 0.505 km³ (409,000 ac·ft).
Though it provides irrigation to 61630 ha for paddy and upland crops, it has aggravated the salinity ingress into the wetland and the river due to reduced outflows during summer months.

Temperatures recorded in the area are a maximum of 27.5 °C (81.5 °F) and a minimum of 25.5 °C (77.9 °F).
The climate is hot and humid during April–May while cool during December–January.
The average annual runoff from the river system into the estuary is reported to be 76 cubic kilometers of freshwater. The basin drainage area is 1,700 km² (660 mi²) and with an average annual rainfall of 2400 mm (94 in) it discharges 3.375 km³ (2,740,000 ac·ft) of flow annually. It acts as a flood storage lake thus protecting the thickly populated city of Quilon (Kollam) and the coastal land. The Kallada dam built across the Kallada river is 85.3 m high by 35 m long (280 ft by 115 ft) with a reservoir area of 23 km² (8.9 mi²) with a storage volume of 0.505 km³ (409,000 ac·ft). Though it provides irrigation to 61630 ha for paddy and upland crops, it has aggravated the salinity ingress into the wetland and the river due to reduced outflows during summer months.
Temperatures recorded in the area are a maximum of 27.5 °C (81.5 °F) and a minimum of 25.5 °C (77.9 °F). The climate is hot and humid during April–May while cool during December–January.
Ashtamudi Lake