The source of the River Conwy is high in the Snowdonian mountains. As air hits the mountains, it is forced to rise. It then cools and condenses and precipitation occurs. Watersheds are the dividing lines of mountain ranges and the areas between them are called drainage basins. Lakes may form over impermeable rock and sphagnum moss will thrive here. Tributaries join together at confluences and the river grows in strength.

Students could be asked to draw a simple drainage basin diagram or label a diagram they have been supplied with. Alternatively, they could identify a drainage basin on a map and label some of the key features.