• Heavy and toxic metals pollute the lake, its sediment and its fish, Raw sewage is also discharged.
• Don't eat the fish, they are filled with heavy metals. ey m
Image: KNA
Heavy and toxic metals are killing Lake Naivasha and the several fish species are disappearing.
Hippos and crocodiles remain.
“In order to safeguard human lives, there is a need to conduct water and fish quality analysis even as the unpredictable phenomenon [of flooding] continues,” the National Environment Management Authority said.
Researchers say the lake is dying a slow death and toxic metals exceed the Health ministry's recommended levels, make the water undrinkable.
Experts say Lake Naivasha, a freshwater lake, has let to pH levels of six to eight, but pollution has led to acidification, making the levels drop below six.
Soil erosion and runoffs pour pesticides into the lake.
A probe established the source of heavy metals in the lake was mostly from farming, urban effluents and beach activities.
Another factor increasing the heavy metals is the fact the lake has been flooded for the last seven years. It's area has increased by about 58 per cent between 2010 and 2013 and is currently 158 square kilometres.
The flooded areas are low-lying riparian land that used to be farmland, public beaches and sewage points, researchers said in a report titled Heavy metals in surface sediments of Lake Naivasha: spatial distribution, source identification and ecological risk assessment.
Sampling points were Kamere beach, Karagita shores, Rivers Malewa and Karati mouths, central and eastern parts of the lake, the southern shoreline, and Crescent Island.
Samples were collected and analysed for heavy metal concentrations at the International Center for Research in Agroforestry soil Laboratory in Nairobi.
The metals at most points were include lead, zinc, chromium, iron, manganese, cobalt and iron.
“In order to safeguard human lives, hotspots of pollution should be marked for intervention even as the unpredictable phenomenon [of flooding] continues,” the scientists said.
The lake has traditionally supported local populations, tourism and a wide range of biodiversity. It includes waterbucks hippos and 350 species of migratory water birds, fish and plant life. It used to provide an income for fisherfolk.
Currently, it is also supporting a vibrant horticultural industry, a growing population of flower farm workers, geothermal energy production, intense fishing and a runaway building boom. Flower and vegetable farms are a significant contributor to Kenya’s economy.
The highest concentrations of all the heavy metals were found in samples collected from south of the lake at Kamere beach and east at Karagita shores. The lowest while lowest concentrations were reported at the north side of the Lake. Elevated levels of manganese were found in the east at Crescent Island.
Some of these heavy metals cause decreased mental, nervous system and physical development in children. In adults, they cause causes high blood pressure, kidney damage and reduced fertility.
Forty-nine per cent of the cent sediments were classified as “unpolluted to moderately polluted” for all heavy metals, except for zinc metal that was categorised as “moderately to strongly polluted".
“Zinc threats to the aquatic ecosystem should not be ignored. Proper management plans need to be put in place; and priority areas for remediation interventions are the central portion of the lake areas, and the south and eastern shoreline that have a high level of metal pollution,” the scientists recommend.
Zinc poisoning causes stomach cramps, nausea, vomiting and diarrhea.
The experts warn that if this goes unmonitored, the extinction of the remaining fish species in Lake Naivasha was imminent.
Researchers included Grace Olando from the Department of Environmental Sciences, Maseno University; Lydia A. Olaka from Department of Geology, University of Nairobi; Philip O. Okinda attached to the department of Chemistry, Maseno University; and Paul Abuom from the Department of Environmental Sciences, Maseno University.
The scientists said the lake has been polluted by the untreated sewage from the treatment plant, which has been partially submerged by the swollen lake.
“The lake flooded parts of the terrestrial land around it increasing in size. The higher concentrations of heavy metals found in the northeast around river mouths and sewage point and the public beach area on southern side of the lake could be linked with effluents from sewage and boating activities, the report read.
Researchers call for repair and maintenance of the sewage plant and disposal of toxic sludge that does not leach toxic metals into Lake Naivasha.They also call for the controlled leaching of toxic materials from former submerged hazardous waste sites in the watershed.
High concentration of lead, chromium, copper, manganese and zinc at the southern shoreline could be linked to the human activities including removal of buffering plants such as papyrus and increased cultivation of the flower farms in the area which have led to high land erosion.
“Higher concentrations of lead, chromium and manganese metals occur on the northern side, at Malewa and Karati river mouths. This can be attributed to the inflow from the rivers and inputs from the catchment into the lake. The anthropogenic sources of zinc in the sediments can be attributed to intense boating activities along the beaches,” the researchers said.
In 2020 the National Environment Management Authority recommended formation of a multi-agency team to study water, sediments and fish quality along the shoreline.
Rising water levels have submerged several facilities that are sources of pollution.