Local efforts are being made to neutralise the breeding grounds of black flies in Ugandan rivers to prevent river blindness infection from spreading.
Certain rivers, which are being treated once a month, are measured and then sprayed with just enough larvacide to kill black fly larvae - and still leaving the treated water fit for drinking.
The black fly larvae tend to also attach themselves to river crabs.
Ephraim Tukesiga, a vector control officer, uses traditional fishing methods to catch crabs to see if they carry the larvae of the black fly.
If the flies are still alive after the chemical treatment, the larvae can be found in the joints of the crab.
Dr Moses Katabarwa, a senior epidemiologist at the Carter Center, works alongside Tukesiga to make sure the local rivers are treated twice a year and monitored.
This is an attempt to break the cycle of infection in the rivers caused by the black fly larvae, while still leaving the water safe for human consumption.
Lifelines: The Quest for Global Health will air on Al Jazeera in 2014.