Watersheds 101

I spent the 4th of July at the Marin County Fair, befriending llamas, riding the Ferris wheel, eating ice cream, and exploring an oversized floor map of Marin watersheds--part of an "Aquatic Adventures" exhibit that The Bay Institute helped to put together for the Fair. It was fun to watch kids and grown-ups alike wander over the map and discover--maybe for the first time--their "place" within the giant jigsaw puzzle of watersheds.

But what exactly are watersheds, and why are they important? Here’s a little "Watersheds 101." (Heads up! There might be a quiz later.)

• A watershed includes all the land that water flows over (or under) as it drains to a particular body of water such as a creek, river, wetland, bay, or ocean. Picture a giant funnel that catches all the rain and snowfall in a particular area and directs it toward the lowest common point. Everything on that land--rocks, forests, buildings, parking lots, wildlife, and people--is also part of the watershed.

• No matter where you live, you live in a watershed. In urban areas, where creeks are often confined to concrete channels or underground culverts, discovering your local watershed may require some detective work!

• Large watersheds are often made up of smaller watersheds, so you may be a citizen of several watersheds all at the same time. (For example, my local watershed--Sister's Creek--is part of the San Rafael watershed, which is part of the San Francisco Bay watershed.)

• The Bay's watershed includes hundreds of neighborhood creeks. But it also includes the Delta, the Central Valley rivers, their tributaries in the Sierra and Southern Cascades, and all the land that drains into each of these waterways. All told the Bay’s natural watershed drains nearly 61,000 square miles--almost 40% of California--and extends south into the Tulare Lake Basin and north into Oregon.

• Why do watersheds matter? You can think of a watershed as a kind of community connected by water; what we do in one part impacts the other parts. For example, runoff from rainfall or sprinkler systems can pick up pollutants in your neighborhood like motor oil, weed killer, and pet waste and carry them to nearby stormdrains and creeks. From there, pollutants can travel downstream and affect water quality in other parts of the watershed. In fact, all kinds of activities--farming, logging, construction, damming or diverting water, driving, gardening, washing your car, taking a bath--can affect the quantity and quality of water in other parts of your watershed.

• Because watersheds are one of the primary ways that nature divvies up the landscape, they are one of the most useful units for conservation planning. Watersheds can span county, state, and even national borders (think of the Mississippi River watershed, which drains all or part of 31 states and two Canadian provinces), requiring us to think across political boundaries to come up with the best solutions for taking care of the land.

Now, time for the quiz: Can you name your watershed(s)? (If you’re not sure, the Oakland Museum of California's creek guide can help.)

Ann Dickinson is Communications Manager for The Bay Institute (www.bay.org), a nonprofit research, education, and advocacy organization dedicated to protecting and restoring San Francisco Bay and its watershed, "from the Sierra to the sea."