MumbaiThe Mithi river that runs 18km through Mumbai’s length was Maharashtra’s most polluted river in 2018, containing human and animal excreta almost 15 times the safe limit.The Maharashtra Pollution Control Board’s (MPCB) water quality assessment of eight major state rivers in 2018 was published in the recent Maharashtra Economic Survey Report 2018-19.The study found levels of faecal coliform content (indication of human and animal excreta) and biochemical oxygen demand (oxygen levels for aquatic life to survive ) of the Mithi river were above the safe limit.A polluted Mithi spells trouble for Mumbai — the 2005 floods that killed more than 1,000 people in the city was caused mainly because the river was clogged. River pollution also poses health hazards to neighbourhoods around it. And, Mithi is not Mumbai’s only polluted river. An independent report by environment group RiverMarch, submitted to the Brihanmumbai Municipal Corporation chief last week said three other rivers — Dahisar, Poisar and Oshiwara — were also highly polluted with plastic, animal waste and carcasses, garbage and sewage from public toilets.Mithi is the state’s most polluted river despite efforts to rejuvenate it for almost two decades. Last week, state environment minister Ramdas Kadam and Yuva Sena chief Aaditya Thackeray announced that the Rs 2,136.89-crore Mithi river rejuvenation project will be completed in the next two years.