The water here reaches the Douro too

The Ouro, Beça and Cavez stream enter the Tâmega on its right bank; the Tâmega is a tributary of the Douro. The municipal environmental report traces this connection between rivers: a map of Cabeceiras continues far beyond the municipality’s boundaries.

A river basin includes the land that channels water through streams and rivers to a shared outlet to the sea. It is more than a blue line on a map. The APA also distinguishes a sub-basin, whose drainage converges on a point in a watercourse, such as a confluence.

In this story’s diagram, names show connections between waterways, not the boundaries of their basins. To understand a river, we need to include the land that supplies its water. That connection leads from tributaries to soil erosion and life along the banks.