Land and water are one system
Un bassin versant rassemble toutes les connexions en amont
A watershed is the land area that drains to a shared waterbody. Rain and snowmelt can travel across soil, streets and fields, through wetlands and streams, or underground before reaching a lake. What happens upstream can therefore matter downstream.
Watershed boundaries follow the shape of the land rather than county lines. Use an official map for a particular lake; do not assume two nearby waters share the same drainage path.