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A watershed is a land area that drains to a common waterway such as a:
In the Santa Clara Valley, rain flows into creeks, rivers, and storm drains that flow to San Francisco Bay. Some of the water infiltrates the soil or is diverted to reservoirs and percolation ponds to replenish underground aquifers. You live in a watershed that flows to a local creek, and all of the runoff from your home, yard and neighborhood flows to that creek.
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When a drop of water falls inside a watershed, it flows toward that main body of water. It can do this in one of two ways: by soaking into the ground, or by running off the landscape directly into the waterbody. If it soaks into the ground, it becomes part of the groundwater supply, which eventually connects with the surface water. When it goes into the ground, the soils filter out harmful pollutants — things like fertilizer, oil, chemicals, bacteria, trash, etc. — so the water stays clean. But if the raindrop can’t soak into the ground, it will run toward the lowest point in the landscape, picking up whatever pollutants it finds along the way. This is called runoff, and it’s a major source of water pollution.
Watersheds are more than just drainage areas in and around our communities. They are necessary to support habitat for plants and animals, and they provide drinking water for people and wildlife. They also provide the opportunity for recreation and enjoyment of nature. Pollution in our watersheds degrades the environment, harms wildlife habitat, impacts the economy and jobs, causes higher taxes and fees, and ultimately can affect the health of humans.
Healthy watersheds provide critical services, such as clean drinking water, productive fisheries, and outdoor recreation, that support our economies, environment and quality of life. Protection of natural resources in our watershed is essential to maintain the health and welfare of all living things, both now and in the future.