Kamburu Dam, Kenya — Alfred Nyaga irrigates his acre of khat, a mild stimulant, in Kaloki village by pumping water with a diesel-powered engine directly from Kamburu Dam in central Kenya.
Each morning, he takes the khat he has harvested at night to sell at Kiritiri market, some 30 km (18.64 miles) from the village on a shrub-covered slope stretching to the hydropower dam's banks.
Being so close to the reservoir means Nyaga and his four workers are often bitten by mosquitoes as they toil.
"We have no other option because we have to work on our farms and we need the dam water," said Nyaga.
The dam provides an ideal breeding environment for the Anopheles mosquito, which carries the malaria parasite, putting local farmers and their families at risk of infection.
Bed nets to keep off the insects while sleeping are a must in the mud and tin-roofed houses that dot the landscape.
Kenya's hydropower dams benefit communities living on their banks by providing a plentiful source of water to irrigate crops.
But the large reservoirs that feed them are also a habitat for mosquitoes, which thrive especially well in the shallow puddles that often form along their shorelines.
African governments and the World Bank argue the continent needs hydropower dams to boost inadequate electricity supplies with a clean, renewable source of energy. Sub-Saharan Africa already has over 2,000 dams.
But a study published last September in Malaria Journal warned that over 1 million people in sub-Saharan Africa would contract malaria in 2015 because they lived near a large dam.
The researchers, including experts from the International Water Management Institute (IWMI), found that construction of an expected 78 major new dams in the region over the next few years would lead to an additional 56,000 malaria cases annually.
Malaria impacts must be tackled so they do not undermine the sustainability of Africa's drive for development, the study warned.
It recommended distributing bed nets to people living within 5 km of dams. It also proposed operating schedules that dry out reservoir shoreline areas where mosquitoes breed at critical times, and introducing fish that eat mosquito larvae.
In Kenya, the state-run Kenya Electricity Generating Company Limited (KenGen) is aware of the problem, but has yet to act.
KenGen, which manages the Kamburu Dam straddling Embu and Machakos counties, says it has not intervened to prevent malaria here or around its other dams, even in high-risk areas.
KenGen operates 14 dams across Kenya, with total power generation capacity of 819 megawatts. They produce more than half the power consumed in the country.
Embu and Machakos have been categorised as low-risk malaria zones despite having the highest concentration of large dams, totalling five between them along the Tana River.
More broadly, malaria is a major health challenge in Kenya, with some 25 million people at risk of the disease, according to 2009 data from the Kenya Medical Research Institute.
Malaria accounts for 30 to 50 percent of all outpatient attendance and 20 percent of admissions to health facilities in the country.
Peter Esekon, a clinical officer at KenGen, said the company undertakes weekly surveillance, and so far has not observed a substantive increase in malaria at any of its dam sites.
Yet while KenGen is not planning action to curb malaria near its dams for now, it is open to suggestions such as those in the recent study, he added.
Meanwhile, county governments are undertaking wider anti-malaria efforts that are helping keep people protected.
Health education among communities living near dams has helped create awareness and reduce malaria cases, officials say. The government also provides bed nets to pregnant mothers and children younger than five in all counties.
Winfred Murigu, a nursing officer at the Machanga health centre near Kamburu Dam, said that besides educating patients at clinics, community health workers visit residents to talk about various issues including malaria.
Public health officers also visit homes when spraying places where mosquitoes breed, she said.
Nyaga has seen community health workers a few times in his area. "They told me about using a bed net and clearing bushes around here to keep away mosquitoes," he said.
His sister-in-law Mercy Ndeki, 45, who lives nearby, had her compound fumigated by officials from Machanga. Afterwards, the mosquitoes disappeared for a while, and the family also uses bed nets bought at the local shopping centre.
Anthony Mwaniki, the nursing officer in charge of Riaciina dispensary near Kindaruma Dam in Embu, said there had been a drop in malaria prevalence thanks to higher awareness.
"At times we receive up to 70 patients with malaria in a month, but this has gone down in the past few months due to the health education we give to patients," he said.
Most malaria patients treated at the Riaciina and Machanga dispensaries live within 5 km of the two dams.
Nyaga, who has another homestead about 8 km from Kamburu, said there were no mosquitoes there compared with his house on the banks of the dam.
KenGen's Esekon said transmission is low around its dams in this area because local people do not travel much, reducing the risk of the parasite being brought into the area.
But KenGen operates hydroelectric plants in other parts of the country that are reported to have high malaria prevalence, such as Sondu Miriu Dam in Nyanza, a malaria-endemic zone in Kisumu County.
In some high-risk zones like Kisumu, the government offers everyone free bed nets.
The IWMI study noted that further research is needed to investigate the potential impact of climate change on malaria around both existing and planned dams in sub-Saharan Africa, including areas that are currently free of the disease.
(Reporting by Anthony Langat; editing by Megan Rowling. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit www.trust.org)