Beneath the glistening water of some parts of the Nairobi River, is a bed of murky water winding through the city’s river meanders. Vendors rinse vegetables on its banks. Children play near its sluggish current. Sometimes, those who totally disregard the environment, dump in the river or at its banks. From a distance, it looks alive. But beneath that surface, scientists say, the river carries a toxic and invisible brew of human waste, industrial discharge, and petroleum residues that tell the story of a city drowning in its own pollution.
In a 2024 study published in Environmental Science & Technology, researchers from the United Kingdom and Kenya used ultrahigh-resolution mass spectrometry to uncover the molecular makeup of the Nairobi River’s sediments. What they found confirmed what residents long suspected the river is more than just dirty; it’s chemically poisoned.
“The sediments of Nairobi’s urban rivers are a molecular diary of human activity,” the study’s authors wrote. “They captured the evidence of untreated sewage, industrial discharge, and complex organic pollutants that accumulate over time.”
The research team collected samples from three points along the river before, within, and after its passage through the informal settlements of Kawangware and Kiambiu. Using a technique called Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT–ICR–MS), they analyzed thousands of organic compounds invisible to the naked eye.
Their findings painted a damning picture. Sediments from mid-slum areas contained high levels of steroid-like molecules such as cholesterol and coprostanol chemical fingerprints of untreated human and animal waste. “We are not just seeing fecal contamination,” explained Dr. George Olaka of the University of Nairobi, a co-author of the study. “We are seeing evidence of detergents, oils, pharmaceuticals, and other chemical residues that are reshaping the river’s chemistry.”
The deeper scientists dug, the more disturbing the picture became. Petroleum-derived compounds including thiophenes and hydrocarbons appeared in high concentrations downstream, particularly near industrial zones. This suggested a cumulative buildup as the river wound its way through the city’s densely populated and industrialized neighborhoods.
RECLAIMING THE RIVER :Nairobi River Regeneration Project (NRRP)
Against this grim backdrop, Kenya embarked on a historic environmental mission: the Nairobi River Regeneration Project (NRRP) a KSh 50 billion program launched in March 2025 by President William Ruto.
The NRRP aims to reclaim the Nairobi, Mathare, and Ngong rivers transforming them from polluted channels into clean, living ecosystems that support urban life.
“The Nairobi River Regeneration Project is a bold step to reclaim the city’s river spine by restoring riparian land, removing solid waste, and improving sanitation,” said Lt. Col. Kahigu Njoroge, the project’s manager. “We are rebuilding Nairobi from its rivers outward creating green spaces, safer neighborhoods, and stronger communities. This is not just about cleaning a river; it is about restoring the city’s dignity and resilience.”
For the first time, Nairobi’s cleanup is being guided by both engineering and evidence. The NRRP combines scientific data including findings from studies like the 2024 research with urban planning and community participation.
Its five pillars include flood control, sanitation, catchment restoration, transport access, and urban landscaping. A flagship intervention is a 60-kilometre trunk sewer line running from Ondiri Swamp in Kikuyu to Ruai, designed to divert untreated waste before it reaches the river.
Additionally, a new wastewater treatment plant in Kariobangi will handle sewage inflows, while stormwater channels and wetlands will naturally filter runoff.
During the Mazingira Day 2025 media tour, journalists witnessed the transformation firsthand. In Dandora, excavators clawed through mountains of waste, revealing stretches of river that had been buried for decades. The scene was both hopeful and haunting a city uncovering its wounds to heal them.
“The Dandora stretch shows what we are up against, but it also shows what is possible,” said Lt. Col. Njoroge. “Clearing this section is about restoring life to a river that has sustained this city for generations.”
The clean-up extends to Kamukunji, City Cotton, and Lucky Summer, where blocked riverbeds are being reopened and banks stabilized with vegetation. Plans include community-managed green spaces and new waste collection points to prevent re-pollution.
The Nairobi City County Government insists that the regeneration’s success depends on residents themselves.
“True regeneration begins with the people,” said Maureen Njeri, County Executive for Green Nairobi. “The communities living along the river are not passive beneficiaries they are partners. Their work in greening, waste management, and advocacy is shaping how we design housing, sanitation, and urban spaces.”
Already, the NRRP has created thousands of green jobs. Youth groups are being trained to manage waste, plant trees, and maintain river parks. In Kamukunji, a new football field and park are emerging where dumpsites once stood.
“Through the Nairobi River Regeneration Project, young people are now involved in tree planting, riverbank clean-ups, and sports instead of crime,” said Josephat Karomi, Chairperson of the Kamukunji Nairobi River Community. “This project is transforming lives, not just landscapes.”
The Nairobi River corridor has been declared a Special Planning Area halting new construction within a 60-metre buffer zone until a comprehensive plan is developed. This legal protection, experts say, is key to breaking the cycle of encroachment and re-pollution.
In two years, city planners hope to unveil an Integrated Development Plan that reimagines the river corridor as a hub for affordable housing, transport, and recreation all anchored in ecological restoration.
The project also integrates 10,000 affordable housing units, modern markets, cycling lanes, and expanded public parks merging environmental and social renewal.
The regeneration effort comes amid growing calls for accountability from industries and developers who have long contributed to the river’s degradation. Environmental advocates argue that true transformation will require strict enforcement of the Water Quality Regulations (2006) and real-time pollution monitoring.
Grassroots organizations also continue to pressure local authorities to ensure transparency in project spending and long-term maintenance.
It is estimated that pollution from the Nairobi River currently affects more than 2.5 million residents, with downstream consequences for ecosystems and infrastructure, including Thwake Dam a critical water source for southeastern Kenya.
Public health experts say the implications extend beyond immediate contamination. Polluted river water contributes to rising cases of diarrhoeal diseases, antimicrobial resistance, and chemical exposures linked to cancers and reproductive disorders.
In a 2022, report by the African Population and Health Research Center (APHRC), at least 66 per cent of the faecal waste in Nairobi is still left untreated. While surface debris can be removed, the deeper toxins require scientific interventions from sediment dredging to ecological restoration and continuous water testing.
By merging science, policy, and community action, the NRRP is being hailed as a potential model for urban river recovery in Africa. If successful, it could restore not just water quality but public trust proving that environmental repair and economic growth can coexist.
“The Nairobi River Regeneration Project is more than an infrastructure plan it is a blueprint for fairness, health, and hope,” said Lt. Col. Njoroge. “Every restored metre of riverbank brings us closer to a Nairobi where clean water, safe housing, and green public spaces are a shared reality for all.”
The pollution that once symbolized decay may yet become a catalyst for renewal if evidence continues to drive action, and if citizens demand accountability.
Scientists warn that pollutants once embedded in sediment can bioaccumulate, moving up the food chain through fish, crops, and livestock. Over time, this exposure may cause gastrointestinal infections, hormonal disruptions, and organ damage.
Earlier studies had flagged high levels of antibiotic residues and pathogens in Nairobi River water, but this latest research offers the clearest molecular evidence yet of long-term contamination.
The Nairobi River has endured decades of degradation. Since the 1990s, scientists and agencies such as UNEP have warned of unregulated dumping and weak pollution controls. Despite numerous clean-up campaigns from the “Adopt-A-River” initiative years back to multi-million-shilling rehabilitation projects pollution persisted, often resurfacing with every rainy season.
