Water Cabinet Secretary Simon Chelugui has disclosed that Nairobi River has more than 4,000 pollutants in it.
Reports have indicated that after this finding the government might order industries to shut down for dumping toxic waste.
According to the County Executive Committee member for Environment Veska Kangogo, the task of reclaiming the now filthy river has been made difficult by big industries which dump waste into it.
She also faulted the Kenya Association of Manufacturers for licensing businesses that dump their waste into the river.
Ms Kangongo noted that a check on the city's drainages, it was discovered that high-end hotels located in Westlands directed raw sewage into the river.
There have been several initiatives to clean up the river, including the demolition of structures built on riparian land.