SLO Watershed

San Luis Obispo County Watersheds

A Watershed Approach

A watershed is the area of land where all of the water that is under it, or drains off of it, goes into the same place. A watershed approach is the most effective framework to address today’s water resource challenges. Watersheds supply drinking water, provide recreation and respite, and sustain life. More than $450 billion in food and fiber, manufactured goods, and tourism depends on clean water and healthy watersheds.

Explore a watershed

Learn About Watersheds

Surfrider: Watersheds 101

Watershed Demo


Let’s start with a simple definition:

A watershed is the area of land that catches rain and snow and drains or seeps into a marsh, stream, river, lake or groundwater.


Here’s a more formal definition:

“The watershed is defined as a unit of natural or disturbed land on which all the water that falls (or emanates from springs) collects by gravity and fails to evaporate and runs off via a common outlet. The watershed is the basic unit of water supply.”

–Peter E. Black, Watershed Hydrology, Second Edition, 1996.


Here’s a more holistic view:

“That area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community.”

–John Wesley Powell, explorer and scientist

Watersheds provide our drinking water, habitat for wildlife, soil in which to grow our food, and the streams, rivers and lakes we use for fishing, boating and swimming. We all share a common interest in having a healthy watershed. (The Center for Watershed Protection)

Homes, farms, ranches, forests, small towns, big cities and more can make up watersheds. Some cross county, state, and even international borders. Watersheds come in all shapes and sizes. Some are millions of square miles, others are just a few acres. Just as creeks drain into rivers, watersheds are nearly always part of a larger watershed. (Conservation Technology Information Center)

In the continental United States, there are 2,110 watersheds. Including Hawaii, Alaska, and Puerto Rico, there are 2,267 watersheds. In San Luis Obispo County, there are 25 watersheds and 264 subwatersheds.

Absolutely! There are many simple steps you can take to positively impact the health of your watershed such as planting a tree, installing a rain barrel, and landscaping with native plants. Here are some more examples of what you can do.

Everyone lives in a watershed. We all have an impact on the health of our watersheds. Our daily actions on our own properties, including how we care for our yards and dispose of our waste, may seem unimportant, but these small actions have can a huge effect across an entire watershed. Use our interactive map to find out which watershed you live in.