Toxic dump: The poisons killing lake Victoria

Lake Victoria covered by algae near the mouth of River Kisat in October 2019. JEFF ANGOTE | NATION

A three-month investigation, Rotting from the Deep, can now reveal why Africa’s biggest freshwater lake is dying a slow death that has seen more than a dozen fish species disappear.

We selected 28 sampling points for this study. These locations were identified due to proximity to contamination through waste discharge or levels of human activity.

The sample locations included the mouths of Migori and Kuja rivers, Homa Bay, River Awach, Kendu Bay, Sondu River, Dunga Beach, Kisat River at the golf club, Usoma Beach, Nyando River and near Kisumu Resort.

We also collected samples at Marenga Beach, River Saka at Kodiaga Prison, River Nzoia near Panpaper’s effluent discharge point and waste from the jaggery factory at Webuye. Other samples were collected at various factory effluent discharge points including those from Kibos Sugar and Kisumu Water and Sewerage Company (Kiwasco). 

We travelled to Uganda and also sampled the Nakivubo channel, which carries waste from Kampala into Lake Victoria. We picked more samples at Gabba area near Kampala, at Masese Beach and in Jinja at the source of the Nile. On the lake, we sampled various places, including the lake deep, lake surface and near the shores.

From all these locations, we collected a total of 54 samples of water, fish and sediments.

Our study showed that the contamination is spreading from the shores heading towards the middle of the lake.

Among the poisons, we found at least eight metals in various concentrations, with the most toxic being 75 times more poisonous than recommended levels.

The metals found in most of the sampling points include lead, mercury, cadmium, chromium, zinc, iron, manganese and fluoride.

Lead was widely distributed, especially in Migori, Kendu Bay, effluent flowing through Nyanza Golf Club, Kodiaga Prison discharge point, Nyando River, Jinja waters, and fish from Masese Beach in Uganda and Marenga Beach in Kenya.

The metal causes decreased mental, nervous system and physical development in children. In adults, it causes high blood pressure, kidney damage and reduced fertility. We also found lead in excessive quantities in the fish imported from China that was being sold in Kisumu City and adjacent towns.


Out of the 28 sampling points comprising the lake and its catchment rivers as well as discharge points and the Nile, River Awach had the highest number (67 per cent) of heavy metals detected at levels above the recommended KS levels. The metals were mercury, lead, cadmium, chromium, iron and manganese.

The second most contaminated was River Kisat that was sampled at the Nyanza Golf Club, with five out of nine (56 per cent) heavy metals including mercury, lead, cadmium, chromium and iron.

This level of contamination could be attributed to, among others, the effluent discharged to the river from the KIWASCO treatment site.

River Migori, at its mouth as well as the discharge point at Kendu Bay, had four out of nine (44 per cent) of the heavy metals detected above the recommended levels. These were mercury, lead, cadmium and chromium.

Mercury detected at River Migori could be as a result of the gold mines that discharge waste into the river.

“Observations made during sample collection showed a lot of negligence in handling of mercury by the gold miners as they use it to process gold. High level of self-exposure with the toxic chemical and its vapour, as well as environmental and water contamination, is rampart in this area,” the research report reads. 

We also found DDT (Dichlorodiphenyltrichloroethane), a banned pesticide that has adverse effects on humans and aquatic animals."

The discharges at Homa Bay and Kisumu Beach had the least number of heavy metals, including cadmium and lead at one out of nine (11 per cent) metals detected above KS recommendations.

In all the water samples tested in the first phase of sampling, cadmium was found in 18 out of 20 (90 per cent) samples at above recommended levels, second was lead at 13 out of 20 (65 per cent), then chromium 11 out of 20 (55 per cent), while mercury and manganese were at four out of 20 (20 per cent).

In the second phase of sampling, all the five water samples had more than 44 per cent heavy metals contamination, the lowest being from the Nile at Jinja.

Seven metals were shown to be occurring at levels above the Kenya recommended levels for drinking water in more than 60 per cent of the samples. These were lead, copper, chromium, zinc, iron, manganese and fluoride.

We also found DDT (Dichlorodiphenyltrichloroethane), a banned pesticide that has adverse effects on humans and aquatic animals. Other pesticides we detected include endosulfan and mirex. These pesticides can cause cancer, mouth ulceration, dysphagia and abdominal pain, among other diseases, if ingested. DDT was banned as a pesticide worldwide under the Stockholm Convention in 2001 after it was discovered to be dangerous to wildlife and the environment.


Pesticides are unlikely to occur in drinking water, according to WHO guidelines. There are therefore no recommended residue levels available for most of them.

In this study, up to 21 different pesticides, including organochlorines, organophosphates and pyrethroids were detected at different concentrations and frequencies in the water samples.

The WHO pesticide evaluation scheme (Whopes) programme approves pesticides for direct application to drinking water for control of insect vectors transmitting disease.

Guideline values are therefore available for a few pesticides as maximum levels in drinking water namely: chlorpyrifos (0.03ppm), DDT and its metabolites (0.001ppm), permethrin (0.30ppm) and pyriproxyfen (0.30ppm). Amongst these, only pyriproxyfen has been approved by WHO for addition to water for public heath purposes.

Some of the pesticides found in the samples analysed from the Lake Victoria and its catchment rivers are of known toxicity to both humans and aquatic life.


The pesticides found include fenitrothion, an organophosphate used as insecticide and which is toxic to aquatic life; chlorofenvinphos, which affects the respiratory system in humans; cyhalothrin, which has been shown to cause irritation of the mucous membrane; and bifenthrin, which is very harmful to aquatic life and has been classified as a possible human carcinogen.

A few of the pesticides in the water have been globally banned due to their toxicity and environmental persistence. These include DDT, which is highly persistent in the environment, very soluble in water, affects reproduction in humans and has been classified as a possible human carcinogen.

Endosulfan, which was globally banned in 2012, is an insecticide and a known neurotoxic, causes birth defects, and has the ability to bio-accumulate.

Another banned pesticide detected was mirex, which is also a bio-accumulator and persists in the environment as an organic pollutant thus affecting aquatic life. It’s a carcinogenic and an endocrine disruptor.

In the first phase, River Kodiaga was found to have the highest number of detectable pesticides with 10 out of 21 (48 per cent), these are benfluralin, linuron, chlorofenvinphos, cyhalothrin, azinphos, oxyfluoren, methoxychlor, DDT, DDE and endosulfan. DDT was detected at 3.49 ppm, which was the most concentrated pesticide detected in water in this study.


River Kisat had the second highest number of pesticides with nine out of 21 (43 per cent) detected and include linuron, bifenthrin, acrinathrin, deltamethrin, cypermethrin, chlorpyrifos, DDT, endosulfan and mirex.

Linuron was the most frequent pesticide in the water samples being detected in 15 out of 20 (75 per cent) samples. Phorate and cyhalothrin were both the second most frequent at eight out of 20 (40 per cent).

The second set of samples had slightly higher levels of contamination with Panpaper effluent having 56 per cent of the pesticides detected, followed by water from Marenga beach. Samples from Jinja had the lowest.

Some of the ten rivers that drain into the lake are also dumping toxins that cause deadly diseases into the lake.

Bacteria that can cause all manner of waterborne diseases was also found in almost every location we tested. Out of 25 water samples, 23 had dangerous bacterial growth with total coliforms at counts above what is allowable by the National Environment Management Authority (Nema).

The contaminated samples — 92 per cent — mean almost the entire lake is polluted by human waste, making it one big regional toilet.

The only safe samples were from River Kuja and the factory effluent at Nyanza Golf Club, which had no bacterial growth.

Collection of Panpaper factory effluent at Nzoia River in November 2019. JEFF ANGOTE | NATION

The results showed that 15 water samples (60 per cent) had both Escherichia coli (E. coli) and other coliforms. Escherichia is a type of bacteria that lives in the intestines.

Most types of this bacteria are harmless and even help keep the digestive tract healthy. However, some strains can cause diarrhoea if one eats contaminated food or drinks fouled water.

Ten (45 per cent) of samples obtained at Kuja River, Homa Bay deep and surface lake, River Awach surface and deep, Kendu Bay surface and deep, Sondu River and factory effluent at Nyanza Golf Club, as well as from the Jaggery factory in Webuye had no Escherichia coli contamination.

The physiochemical properties of the same water were tested and most of the water samples were found to have high levels of organic waste evidenced by the high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) levels in 90 per cent and 30 per cent of the samples, respectively.

COD is a measure of the capacity of water to consume oxygen during the decomposition of organic matter. BOD, on the other hand, refers to the amount of dissolved oxygen that aerobic organisms need in order to break down organic material in water over time.


On physical properties, lake water at Homa Bay was the worst, failing in half of all the eight parameters of being compliant with the Kenyan standards.

These were BOD, COD, nitrate and ammonia, an indication of organic waste discharge. Coming second were lake water at Kendu Bay, River Sondu mouth and lake water at Kisumu beach with 38 per cent noncompliance.

Fish samples were tested for the presence of heavy metals, and all of them were found to have at least seven different heavy metals.

These metals occurred at different concentrations and frequencies, and include lead, cadmium, chromium, zinc, iron, copper and manganese. The good news is that some of the heavy metals were detected at levels that are safe for consumption. 

Fish samples collected at Marenga beach in Kenya, Masese and Gabba beaches in Uganda as well as fish from China bought from a supplier in Kisumu had lead at levels far above the recommended level of 0.1ppm. This made them unfit for human consumption.

The same fish samples had relatively high levels of zinc though below the maximum residue level (MRL), which is the highest level of residue tolerated in food. One fish sample obtained at Dunga beach had mercury at 0.03 mg/Kg (ppm), making it unfit for human consumption.

All the four fish samples in these locations had lead at levels above CODEX (FAO/WHO) permitted maximum levels."

The tolerable intake for methyl mercury, which is the form of mercury found in fish as established by World Health Organization (WHO) is 1.6 per kilogramme. But this would still be high if consumed by individuals with a body weight of 10 kilogrammes or less. 

All the four fish samples in these locations had lead at levels above CODEX (FAO/WHO) permitted maximum levels.

We also detected 33 different pesticides in fish samples obtained from the Lake Victoria basin. Only pesticides were detected in safe levels.

Some of those detected include trifluralin at MRL of 0.001ppm (detected at 0.01ppm in Sondu and Homa Bay) marathion at MRL of 0.005 ppm (detected at 0.005ppm in Homa Bay), biphenyl at MRL of 0.01 (detected at 0.07 ppm in Homa Bay), phorate at MRL of 0.01 ppm (detected at 0.04 and 0.03 ppm from Dunga and Usoma beaches, respectively).

Hexachlorobenzene at MRL of 0.01 ppm was detected at 0.09 ppm (nine times more than the recommended 0.01 ppm) from Homa Bay, while pyrazophos was detected at 0.021, 0.025, 0.026 and 0.07 ppm at Dunga, Sondu, Kendu Bay and China fish, respectively, against MRL of 0.01ppm.


In fish samples in Uganda, we detected a total of 19 different pesticides contaminating the fish at an average concentration of 0.095ppm. The highest pesticide was phenothrin at 1.47 ppm. However, there are no guidelines on what levels can be tolerated in food or be harmful to the body.

The most frequent pesticide detected in fish was pyridaphenthion at 80 per cent prevalence while linuron, pyrazophos and cypermethrin were each detected in three out of the five fish samples tested. This translates to a prevalence of 60 per cent.

Sediments, on the other hand, had seven heavy metals detected with none having mercury.

There are no guidelines available for concentrations in sediment.


In the sediments, 25 different pesticides were detected at varying concentrations and frequency. Though no guidelines are available for this type of sample, some pesticides were detected at high levels.

Sediments from an industrial effluent sampled at Nyanza Golf Club, which are from River Kisat and River Sondu, had the highest number of pesticides at nine out of the 25 detected from each.

The pesticides found were resmethrin, benfluralin, tefluthrin, bifenthrin, cyhalothrin, pyrazophos, trifluralin, deltamethrin, biphenyl, hexachlorobenzene and permethrin which was the most concentrated in all the sediments at 12.5 ppm.

Deltamethrin was detected in all the 16 (100 per cent) sediments, while biphenyl was in 13 out of 16 (81 per cent) of the samples, followed by bifenthrin and hexachlorabenzene that were both found in 12 out of 16 (75 per cent) of the samples, ethalfluralin was found in (56 per cent) while others were below that, the least being detected in only one sediment sample.