The river Amba originates in the Borghat hill of the Sahyadri ranges near Khopoli-khandala road at an altitude of about 554 m. Initially, the river flows in the South direction and then turns further into the North West direction till it joins the Arabian Sea in Dharmatar creek near village Revas. The total length of the river is about 76 km before joining the sea.
The river is affected by tidal effect of the Arabian sea (backwater effect) up to Chikan village located at about 31 km from Arabian Sea. The CWC Hydrological Observation site is located at Nagothane about 2 kms up-stream of backwater-affected area. Also due to the existence of K.T. weir at about 1.5 km down-stream of the site, the backwater effect of sea has no influence on the site.
The catchment of the river up to site from its origin is 420 sq km. and is free from backwater. The length of the river up to the site is 41 km There is no structure in the up-stream of the river and the flow is seasonal.