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Watersheds 101

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A watershed is the area of land where all of the water that drains off of it goes into the same place. Storm water, or rain runoff, flows downhill to a nearby waterway. A waterway can have many names such as: gutter, creek, stream, brook, wash, channel, ditch, and river. Smaller waterways, such as creeks, usually join into larger ones, such as rivers, as the water continues to merge on its way downhill. Waterways ultimately carry runoff to large bodies of water such as lakes, reservoirs, bays, and the ocean.

Why are watersheds important?

Watersheds are important because we all live in one! Activities that a person does in one part of a watershed can affect another person, plant or animal in another part of the same watershed. All storm, residential and agricultural runoff ultimately ends up in the same location in a watershed and all of the pollutants in the runoff are carried along the waterways and into a lake or ocean.

When one person dumps motor oil into a storm drain, for example, that same oil will show up many miles downstream. The same is true for pesticides, fertilizers, cat litter, dirt and any other water pollutant you can name.

The Santa Margarita River Watershed

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If you are standing near the County of San Diego’s Park in Rainbow, CA or in the northern portion of Fallbrook, CA, you are in the Santa Margarita River Watershed! Rainbow Creek is a part of the watershed, meaning all of the water flowing in Rainbow Creek makes its way to the Santa Margarita River, eventually emptying in to the Pacific Ocean.

The Santa Margarita Watershed is unique! It is the least disturbed river system on the Southern California Coast. It is the longest free-flowing river and its 27 miles of contiguous riparian habitat makes it one of the highest priority rivers in both San Diego County and Southern California!

 The Santa Margarita River is formed by two major tributaries: Temecula Creek and Murrieta Creek. Other tributaries, such as Rainbow Creek, Coahuila Creek, and De Luz Creek also flow into the river. The Santa Margarita River drains approximately 742 square miles within Riverside and San Diego Counties.


Today, San Diego County is home to over 3 million people with about 70 percent of our water being imported from the Colorado River and northern California. Yet, some farms and facilities still use water from the Santa Margarita River. In fact, most of the drinking water on Camp Pendleton is from wells that are primarily recharged by river water!

How can you help make sure that the watersheds remain healthy?

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  • The only item that should enter storm drains, creeks, and other drainages is rain! Water from storm drains is not treated—it flows directly to the ocean.
  • Always follow the instructions on household chemicals, pesticides, and fertilizers carefully. Over applying chemicals can cause serious harm to our watersheds.
  • Reduce, reuse, & recycle! Trash can make its way to our waterways and can not only be ugly, but it also causes damage to the ecosystem.
  • Properly dispose of yard waste—including soil– as debris can clog waterways and carry potentially hazardous materials along with it.
  • Pick up after your pets. Pet waste is full of nutrients and bacteria that are bad for our watershed’s health.

In addition to people, many plants and animals call the Santa Margarita River watershed home! Here are just a few of the special animal species that live in the area.

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Western Scrub Jay
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Southwestern Pond Turtle