The Mithi River (aka Mahim River) is a river in Salsette Island, the island of the city of Mumbai. It is a confluence of tail water discharges of 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 in other times. During this season the river is a favourite with the anglers who catch large fish that have escaped from the lakes. Fishing is banned there.
The river is also a natural drainage channel which carries the excess waters during the monsoons. However it is filthy mainly due to the presence of slums and the discharge of industrial effluents.
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 15 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 m in the upper reaches, has been widened to 25 m in the middle reaches and up to 70 m in the lower reaches after the 26 July 2005 deluge (944 mm in 24 h on 26 July 2005).
It is also less well known that the Mahim bay area, where Mithi River meets Arabian Sea is a nominated bird sanctuary where migratory birds come for nesting. This part is full of mangroves. When the river was not as polluted as it is today, it used to serve as an important storm water drain for Mumbai but as it has been used as a sewer over the years, its importance as a storm water drain has reduced and on the contrary, it poses as a hazard during high tide bringing polluted water into the city.
Very often, and this continues to happen, citizens dump raw sewage, industrial waste and municipal waste into the river, unchecked. 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.
In 2006, the Supreme court of India passed an order directing the state government to remove encroachments on all water bodies .
An environmental group has been formed by Rajendra Singh, an award winning conservationist in 2009. It aims to revive the dying river.
Many young entrepreneurs in and around Mumbai are now aggressively involved with cause of Mithi River, and creating awareness on a global scale as the government of India has once again started ignoring this extremely important issue. In 2009, environmentalist and Magsaysay Award winner, Rajendra Singh lead a yatra, of a group of environmentalist and NGOs, through Mumbai city along the endangered Mithi river to highlight its problems.
Recently a Contemporary Art show was held to create major awareness about dire situation of Mithi River in Bombay by "Chintan Upadhyay" titled Khatti - Mithi