Figure 1.

Simplified map of the study area (Aare river system between Lake Thun and the city of Bern, the Aare is the outlet of Lake Thun). Adults were sampled in Aare, Worble, Giesse, Gürbe, Kiese, Müsche, and Rotache (see Supporting Information Table S1 for sampling dates). Circles indicate the location of sewage treatment plants and their gray value the percentage of treated effluent in the river or stream at low flow (%). Shades of gray indicate the human population density (inhabitants/hectare). The box in the upper right inlet indicates the location in Switzerland. Adapted from a map produced by the Swiss Confederation in collaboration with the cantons (www.map.geo.admin.ch, downloaded on November 1, 2018)