what is a watershed?

How do they function?

why are they important?

The health of a watershed impacts the health of the body of water it drains into because conditions upstream have the potential to either positively or negatively affect conditions downstream. Ideally, a healthy watershed is one that is minimally disturbed by human activities, has diverse and connected aquatic and riparian habitats, and supports natural ecological processes and biological communities. Unfortunately, people have altered watersheds all across the world with agriculture, urbanization, mining, and recreation. Changing the environment in these ways creates stressors that directly or indirectly impact individual organisms, their populations and the ecosystem.  By consistently monitoring our rivers and lakes, we can develop ways to mitigate our negative impacts on the environment and restore systems to a more natural state. 

Photo Credit: Gláuber Sampaio

Photo Credit: Ashley Ingnanta

Photo Credit: David Ballew

Image by Rostyslav Savchyn

A watershed is an area of land that captures and drains (sheds) water into a specific body of water, such as a river or a stream. The ridges of highest elevation that separate waters flowing to different rivers or basins make up the watershed boundary. The term drainage basin is sometimes used interchangeably with watershed.

A watershed can be as small as the area that feeds a creek or watersheds can be made up of many smaller watersheds that all drain into a larger common water body.  

Rattlesnake Creek flows into the Clark Fork River so its watershed  becomes part of the Clark Fork  watershed. The Clark Fork River empties into Lake Pend Oreille in Idaho and from there the water enters The Pend Oreille River which then flows into the Columbia River. So, Rattlesnake Creek, the Clark Fork River and the Pend Oreille River watersheds all are part of the larger Columbia River watershed. 

If you think of watersheds as being like a living body, then the water flowing through a watershed is a lot like the circulatory system of the body. Rivers and streams carry water throughout the entire watershed, delivering oxygen and nutrients while transporting out wastes.

The water cycle is the driving force of this system and the sun is the driving force behind the water cycle. It starts when heat from the sun causes surface water to evaporate. As the water vapor rises into the atmosphere it begins to cool and condense in clouds. Eventually, it falls back to the surface as rain, snow or hail. From there the water either soaks into the ground, runs off into a stream or river, or evaporates back into the air.

Image by Gláuber Sampaio

Surface water is the most visible part of the water cycle so it is often what we think of the most when we think about the water in our watershed. It provides habitats for plants and animals, shapes the landscape through erosion and sediment deposition, and is a major source of water for wildlife and humans. Most of our water use comes from surface water. It also serves as a link between the subsurface and the atmosphere.

Image by Ashley Inguanta

When water soaks into the ground it can be absorbed by plants or it can travel downward through the gaps and cracks between soil particles and rocks beneath the surface to become part of an aquifer. Groundwater is used for irrigating crops, mining and industrial activities and is a large source of drinking water. It also serves as a source of recharge for rivers, lakes and wetlands.

Image by David Ballew

The atmosphere holds a lot of water and can quickly transport that water long distances depending on wind currents. Water vapor is one of the main sources of heat transfer from the earth’s surface to the atmosphere. When water vapor condenses, it releases the heat it absorbed at the surface back into the atmosphere – a major driving force for weather patterns.

Photo Credit: Rostyslav Savchyn