Fraser Basin Council


2.3 An Introduction to Watersheds

Everything in the natural world is connected to other parts. Changes made to one element of a system affect many other elements and/or process throughout the system. A watershed—an area of land that contributes runoff to a lake, river, stream, estuary or bay—is a complex and dynamic natural system. Changes to land cover in upland regions of a watershed affect downstream hydrology; waste inputs from one community can affect water quality further downstream. Impacts to an aquifer, such as water withdrawal, may ultimately affect the flow and health of a nearby stream. The various resources that interact within a watershed—the land, the surface and ground water, the air and the organisms within the watershed—cannot be considered in isolation. By recognizing the interconnections between the components of a watershed and by integrating this understanding into planning and decision making within and across watershed boundaries, negative human impacts on watershed health are more likely to be more effectively managed.

Figure 1 – The Components of a Watershed5

Understanding the hydrologic cycle is critical to understanding how a watershed functions. While both salt water and freshwater are essential parts of the water cycle, the freshwater that we use on a daily basis for drinking water, irrigation, and other uses comprises only 1% of all water on Earth. This small proportion of water is “recycled” through the hydrologic cycle, year after year, through oceans, rivers, rain and the atmosphere (Figure 1).

When water falls to the earth as either rain or snow, it either:

  • soaks into the ground
  • flows over the surface of the land into a stream, lake, wetland or the ocean, or
  • returns to the atmosphere through evaporation.

The rate of infiltration within a watershed is determined by many factors, including soil permeability, rate of precipitation and the amount and type of vegetation cover on the land surface. Human activity can alter the rate of infiltration by changing the surface of the land. When rain falls or snow melts too fast to allow for infiltration, or when the ground is too hard (impermeable) for infiltration to occur, such as in an urban environment, the water flows over the land as surface runoff (also called overland flow). Surface runoff is evident within a watershed as streams, rivers, lakes, ponds, wetlands and drainage ditches.

Water that infiltrates into the ground can take one of several routes:

  • Plant roots may absorb the water, which will be used for photosynthesis. This water will eventually leave the plant through the leaves, transpiring back into the atmosphere.
  • Water that is not taken up by plants percolates downwards through the soil to the fully saturated zone at the level of the water table, where it becomes groundwater. Significant collections of groundwater are called aquifers. Aquifers are sometimes tapped with wells for drinking or irrigation. Groundwater may eventually flow back to the surface as a spring or through sub-surface pathways into streams, rivers or lakes.

The areas where precipitation or surface water infiltrates the soil and enters the groundwater system are known as recharge areas. They are often in upland areas of a watershed but may also be in low-lying valleys and floodplain areas. As water evaporates from collecting water bodies, it is returned to the atmosphere, and the cycle repeats itself. No new water is produced: the water that we use today is the same water that existed billions of years ago. How we develop and manage the land within our watersheds ultimately affects the quality of the water that is available for use. In the same way that streams and rivers flow through a collecting basin, the impacts of human activities also flow through a watershed.

It should be acknowledged that there are many different scales of watersheds. The scale of watershed that is appropriate to effectively plan for, and manage, a given issue (or issues) will depend on the nature and scope of those issues and the purpose and scope of the planning process.

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About Rethinking our Water Ways

This website is a guide to help BC communities learn more about planning for local watersheds and water resources, navigate current planning processes, consider relevant issues and challenges — including regional climate change impacts —  and build capacity to develop and implement plans.


The Rethinking our Water Ways guide and website are possible thanks to funding support from the BC Ministry of Environment and Natural Resources Canada's Regional Adaptation Collaborative Program. The guide and website were launched and distributed through a series of regional workshops throughout BC, with funding contributions from the Fraser Salmon and Watersheds Program, Environment Canada and the Real Estate Foundation of BC. Learn more about our funders and advisors.

We want to hear from you

Share your suggestions for this website, and ideas for future water workshops, with:

Steve Litke
Senior Program Manager
T: 604 488-5358

About the Fraser Basin Council

Rethinking our Water Ways is an initiative of the Fraser Basin Council (FBC), a charitable non-profit society that advances sustainability in the Fraser River Basin, across BC, and beyond. Established in 1997, FBC brings people together from multiple sectors to learn about sustainability and find collaborative solutions to current issues. Learn more about FBC by visiting