How watersheds work

A watershed is a process.
Not just a place. 

Every raindrop, every snowflake that falls into our watershed is on a journey. And everything in its path plays a role.

The watershed process is an intricate balance of four key factors: filtration and storage, erosion control, flood attenuation and habitat. But when outside forces—from human intervention—interfere, this natural process is often impeded.


Watersheds collect snowmelt and rainfall as water. Some gets stored in the ground, some runs off.


These hardworking natural filters protect and enhance our water by removing pollutants, preventing soil erosion and storing potential floodwaters.


In addition to providing wildlife habitats, forests moderate climate, play a key role in the hydrologic system, prevent erosion and absorb carbon dioxide.

Creeks and streams

Drop by drop, water is channeled from creeks and streams into soil, groundwater, rivers, lakes and (eventually) oceans.

Roads and buildings

Human-made structures—roads, buildings, dams—alter the landscape and affect how water flows and percolates into the ground.