evidence: Three main areas involved in the five surveys namely (1) mainland coast (Ungoye), (2) large island (Mfangano Island) and small islands [(3) Takawiri, (4) Kibuogi and (5) Ngodhe)]. In large island of Mfangano, eight catchment points were sampled and grouped into three study sites i.e. east coast [(a) Ramba, (b) Wakinga and (c) Mrongo], highland [(d) Kagungu and (e) Gulwe] and west coast [(f) Wakula, (g) Ugina and (h) Ringiti Island]. The map was created with ArcGIS software, version 10.4, http://www.esri.com. [...] There were eight catchment points on Mfangano: Ramba, Wakinga and Mrongo along the east coast (HDSS, population 1642), Kagungu and Gulwe in the highland (HDSS, population 827), and Wakula, Ugina, and Ringiti Island in the west (HDSS, population 1936). These catchment points were selected to represent the different local environments found on the island, from the lakeshore lowland areas to the central highland areas.