National Environment Management Authority (Nema) has shut down four companies in Nairobi's Industrial Area for discharging life-threatening waste into Nairobi River.
The companies shut include Modern Lithographic (K) Ltd, Apex Limited that manufactures paints, Thorlite Kenya Ltd and Kamongo Paper Recycling Company.
According to Nema Director General Mamo B. Mamo, Kamongo Company does not have efficient waste water treatment plant.
"Kamongo company has been discharging into the environment without treating their waste water to the public sewer," said Mr Mamo.
Nema officials also visited Chloride Exide company and gave them 'improvement orders'.
"We have given them improvement orders. We have looked at their records, air pollution emissions and we are doing further tests to ascertain whether they are in line with our regulations," he said.
Nema raided the companies following an expose by Nation on pollution of Nairobi River.
The two-month river pollution investigative project, dubbed "Toxic Flow", trailed the river from Kiambu County where it starts, through Nairobi, Machakos, Makueni, Taita Taveta and Kilifi counties, until it exited into the Indian Ocean at Sabaki Bridge.
According to the report, Nairobi River is suffocating with a cocktail of raw, untreated sewage from everywhere, including some lavish estates in Nairobi.
More than 4,000 slum dwellers have encroached on its path and exploit its water for domestic and pollution-heavy commercial purposes, transforming the stream into a large open sewer.
It is a dumpsite for dozens of industries dotting the city under the sun, which haul into it fresh pollutants every day.
The national environment management agency is expected to continue with the inspection of high risk facilities in Industrial area on Tuesday.
"As precautionary measures we will be closing down facilities that do not meet the set effluent standards," said Mr Mamo.
This comes a day after the World Bank warning that lack of clean water is impediment to economic growth of a country by a third.
Through its report, "The Invisible Water Crisis", the bank says a combination of bacteria, sewage, chemicals and plastics can suck oxygen from water supplies and transform water into poison for humans and ecosystems.
The report says about 1,000 new chemicals get into the environment every year and 80 per cent of the world's waste water is released without treatment.
About 30 to 50 per cent of nitrogen applied to soils leaches into rivers and the air, suffocating aquatic life, worsening climate change and shortening lives through contamination.