Why do rivers in mountains often have clear, cold water compared with lowland rivers?

High-elevation rivers often begin near snowfields, glaciers, or cool springs, which keeps their temperature low. The steeper terrain can move water quickly, leaving less time to warm up. Many mountain catchments also have exposed bedrock and coarse gravel rather than the fine clay common in lowlands, so the water contains fewer suspended particles. That combination makes mountain rivers look clear and feel cold. By the time rivers reach plains, they often warm and collect more sediment from soils and tributaries.