The Mithi River (Pronunciation: [miʈhiː]) is a river on Salsette Island, the island of the city of Mumbai, India. It is a confluence of tail-water discharges of the Powai and Vihar lakes. The river is seasonal and rises during the monsoons. The overflowing lakes also contribute to the river flow, which is stopped by a dam at other times. During this season, the gutter is a favourite with anglers, who can catch large fish that have escaped from the lakes. Chattrapati Shivaji Maharaj International Airport is located right next to the section of river at Andheri (E).
The river originates from the overflow of Vihar Lake and also receives the overflows from the Powai Lake about 2 km later. It flows for a total of 18 km before it meets the Arabian Sea at Mahim Creek flowing through residential and industrial complexes of Powai, Saki Naka, Kurla, Kalina, Vakola, Bandra-Kurla complex, Dharavi and Mahim.
The river has an average width of 5 metres in the upper reaches, has been widened to 25 m in the middle reaches and up to 70 m in the lower reaches after 26 July 2005 deluge (944 mm in 24 h on 26 July 2005).
The river has been polluted by dumping of raw sewage, industrial waste and municipal waste into the river. Besides this, illegal activities like washing vessels, animals and oily drums, discharge of unauthorised hazardous waste are also carried out along the course of this river. Cattle sheds in some areas contribute animal waste. Barrel cleaners, scrap dealers and others dump sludge oil, effluent and garbage in the river. The organic waste, sludge and garbage dumping has reduced the carrying capacity of the river. The water with mixture of sewage and industrial waste is a threat to marine life. The river bed is full of sludge, garbage and vegetation growth like water hyacinth in many parts.
The city of Mumbai earned the epithet – 'Cottonopolis of India' due to its vibrant cotton textile mills. The mills over the years have utilized water from this river and dumped their waste into it leading to the present polluted state of the river.